Science.gov

Sample records for gas phase nucleation

  1. Gas Hydrate Nucleation Processes

    NASA Astrophysics Data System (ADS)

    David, R. E.; Zatsepina, O.; Phelps, T. J.

    2003-12-01

    The onset of gas hydrate nucleation is greatly affected by the thermal history of the water that forms its lattice structure. Hydrate formation experiments were performed in a 72 liter pressure vessel by bubbling carbon dioxide through a 1 liter column at hydrate formation pressures (1.4 to 3.7 MPa) and temperatures (275.0 to 278.0 K) to quantify this effect. They show that when even a fraction ( e. g. 20 %) of the water in which hydrate has formed was recently frozen and thawed, the overpressurization for nucleation was reduced by an average of 50 % versus experiments performed in distilled water. In those experiments where a lower overpressure is present when hydrate nucleated, they tended to form on the surface of bubbles, whereas when a higher amount of overpressure was necessary for hydrate to nucleate, they appeared to form abruptly on bubble surfaces as well as from the bulk liquid phase. In approximation of classical nucleation, hydrate formation could be described as occurring by the spontaneous joining together of arising components of the hydrate lattice. In water that was frozen, and kept at a low temperature (< 275 K), molecular simulation models predict the predominance of water molecules organized as penatmeters, a possible subunit of the hydrate lattice. Our results suggest that in nature, initiation of hydrate formation may be strongly influenced by temperature dependant pre-structuring of water molecules prior to their contact with gas.

  2. Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides

    NASA Technical Reports Server (NTRS)

    Collins, J.; Rosner, D. E.; Castillo, J.

    1992-01-01

    A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

  3. Numerical analysis of an impinging jet reactor for the CVD and gas-phase nucleation of titania

    NASA Astrophysics Data System (ADS)

    Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

    1994-06-01

    We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

  4. Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

    1994-01-01

    We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

  5. Gas-Phase Nucleation in GaAs Thin Film Preparation by Metal Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Okuyama, Kikuo; Huang, David D.; Seinfeld, John H.; Tani, Naoyuki; Matsui, Isao

    1992-01-01

    GaAs epitaxial film growth in the metal organic chemical vapor deposition (MOCVD) horizontal reactor was analyzed by a mathematical model, which takes into consideration of vapor phase hydrodynamic and kinetic phenomena including decomposition reactions of reactants, Ga or GaAs nucleation and subsequent particle growth. The position dependent changes in mass concentrations of Ga or GaAs monomers and homogeneously nucleated Ga or GaAs particles are predicted under various substrate temperatures. The appearance of particles in the gas phase is found to be enhanced under substrate temperature exceeding about 900 K. The conditions under which the growth of the thin film is governed by the diffusive deposition of metal organic vapor and Ga monomers are determined, and the effect of homogeneously nucleated particles on the growth of thin film has been clarified. The simulation results are in good agreement with the data of van de Ven et al [J. Cryst. Growth 76 (1986) 352].

  6. Phase nucleation in curved space

    NASA Astrophysics Data System (ADS)

    Gmez, Leopoldo R.; Garca, Nicols A.; Vitelli, Vincenzo; Lorenzana, Jos; Vega, Daniel A.

    2015-04-01

    Nucleation and growth is the dominant relaxation mechanism driving first-order phase transitions. In two-dimensional flat systems, nucleation has been applied to a wide range of problems in physics, chemistry and biology. Here we study nucleation and growth of two-dimensional phases lying on curved surfaces and show that curvature modifies both critical sizes of nuclei and paths towards the equilibrium phase. In curved space, nucleation and growth becomes inherently inhomogeneous and critical nuclei form faster on regions of positive Gaussian curvature. Substrates of varying shape display complex energy landscapes with several geometry-induced local minima, where initially propagating nuclei become stabilized and trapped by the underlying curvature.

  7. Fission gas bubble nucleated cavitational swelling of the alpha-uranium phase of irradiated U-Pu-Zr fuel

    SciTech Connect

    Rest, J.

    1992-04-01

    Cavitational swelling has been identified as a potential swelling mechanism for the alpha uranium phase of irradiated U-Pu-Zr metal fuels for the Integral Fast Reactor being developed at Argonne National Laboratory. The trends of U-Pu-Zr swelling data prior to fuel cladding contact can be interpreted in terms of unrestrained cavitational driven swelling. It is theorized that the swelling mechanisms at work in the alpha uranium phase can be modeled by single vacancy and single interstitial kinetics with intergranular gas bubbles providing the void nuclei, avoiding the use of complicated defect interaction terms required for the calculation of void nucleation. The focus of the kinetics of fission gas evolution as it relates to cavitational swelling is prior to the formation of a significant amount of interconnected porosity and is on the development of small intergranular gas bubbles which can act as void nuclei. Calculations for the evolution of intergranular fission gas bubbles show that they provide critical cavity sizes (i.e., the size above which the cavity will grow by bias-driven vacancy flux) consistent with the observed incubation dose for the onset of rapid swelling and gas release.

  8. Nucleation separator for flue gas

    SciTech Connect

    Roberts, D.L.

    1988-04-05

    A process for removing particulate compounds and hygroscopic compounds and elements all of which are known herein as contaminants, from combustion flue gas is described, comprising the steps of: (a) treating the flue gas with water until a state of saturation is reached; (b) passing the saturated flue gas into a chamber called herein a nucleation chamber, where cold gas or atmospheric air cools the saturated flue gas below its dew point, causing a state of supersaturation throughout the chamber and a subsequent condensation on the contaminants where contaminant particles serve as condensation nuclei, termed herein as nucleation, and a subsequent growth and accretion of resulting water droplets to droplets of larger size; (c) passing and cooling the flue and droplets through a heat exchanger such as a common gas to liquid type.

  9. Molecular dynamics simulations of cluster nucleation during inert gas condensation

    NASA Astrophysics Data System (ADS)

    Krasnochtchekov, Pavel; Averback, R. S.

    2005-01-01

    Molecular dynamics simulations of vapor-phase nucleation of germanium in an argon atmosphere were performed and a unexpected channel of nucleation was observed. This channel, vapor-induced cluster splitting, is important for more refractory materials since the critical nucleus size can fall below the size of a dimer. As opposed to conventional direct vapor nucleation of the dimer, which occurs by three-body collisions, cluster-splitting nucleation is a second-order reaction. The most important cluster-splitting reaction is the collision of a vapor atom and a trimer that leads to the formation of two dimers. The importance of the cluster-splitting nucleation channel relative to the direct vapor nucleation channel is observed to increase with decreasing vapor density and increasing ratio of vapor to carrier gas atoms.

  10. Grain Nucleation and Growth During Phase Transformations

    NASA Astrophysics Data System (ADS)

    Offerman, S. E.; van Dijk, N. H.; Sietsma, J.; Grigull, S.; Lauridsen, E. M.; Margulies, L.; Poulsen, H. F.; Rekveldt, M. Th.; van der Zwaag, S.

    2002-11-01

    The mechanical properties of polycrystalline materials are largely determined by the kinetics of the phase transformations during the production process. Progress in x-ray diffraction instrumentation at synchrotron sources has created an opportunity to study the transformation kinetics at the level of individual grains. Our measurements show that the activation energy for grain nucleation is at least two orders of magnitude smaller than that predicted by thermodynamic models. The observed growth curves of the newly formed grains confirm the parabolic growth model but also show three fundamentally different types of growth. Insight into the grain nucleation and growth mechanisms during phase transformations contributes to the development of materials with optimal mechanical properties.

  11. Nucleation and growth of Nb nanoclusters during plasma gas condensation

    SciTech Connect

    Bray, K. R.; Jiao, C. Q.; DeCerbo, J. N.

    2013-06-21

    Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

  12. Nucleation

    PubMed Central

    Vekilov, Peter G.

    2010-01-01

    Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution–crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters. PMID:21132117

  13. Nucleation and growth of Mg condensate during supersonic gas quenching

    NASA Astrophysics Data System (ADS)

    Koo, A.; Brooks, G. A.; Nagle, M.

    2008-05-01

    A one-dimensional model based on classical nucleation and growth has been developed as a diagnostic tool for predicting the impact of different process conditions and nozzle geometries on particle size distributions produced from supersonic quenching of magnesium vapours. The model was validated against experimental data for water and SF 6, showing good qualitative agreement with the data. For the cases in the studymagnesium concentration from 1 to 20 mol% and the inlet temperature varying from 1600 to 1900 Kthe model predicts that 99% of the condensation is due to growth of particles nucleated during an initial high nucleation rate stage. The ultimate average particle size is therefore dependent on the magnitude of the nucleation rate during that initial stage of nucleation and to the degree of subsequent growth of those particles which are, in turn, a complex function of the conditions in the nozzle. The distribution of condensate size is somewhat sensitive to the inlet temperature of nozzle, increasing the temperature from 1600 to 1900 K increases the mean size of the condensate by 25%. The molar concentration of magnesium in the gas affects the final particle size but this does not follow a simple trend. The size distribution of particles predicted from the model is very sensitive to changes in surface tension and sticking coefficient, highlighting the need for a more rigorous treatment of these parameters.

  14. Gas-liquid nucleation in a two dimensional system.

    PubMed

    Santra, Mantu; Chakrabarty, Suman; Bagchi, Biman

    2008-12-21

    We study the nucleation of liquid phase from a supersaturated vapor in two dimensions, where the particles interact through Lennard-Jones (LJ) pairwise potential. Using different Monte Carlo simulation methods, we calculate the free energy barrier for nucleation, the line tension, and bulk densities of equilibrium liquid and vapor phases, and also investigate the size and shape of the critical nucleus. The study is carried out at an intermediate level of supersaturation (away from the spinodal limit). In two dimensions, a surprisingly large cutoff (r(c) > or = 7.0sigma, sigma is the diameter of LJ particles) in the truncation of the LJ potential is required to obtain converged results. A lower cutoff [typically 2.5sigma which is generally sufficient in three dimensional (3D) studies] leads to a substantial error in the values of the line tension, nucleation barrier, and characteristics of the critical cluster. It is found that in two dimensions, the classical nucleation theory (CNT) fails to provide a reliable estimate of the free energy barrier. It underestimates the barrier by as much as 50% at the saturation ratio S = 1.1 (defined as S = P/P(C), where P(C) is the coexistence pressure) and at the reduced temperature T(*) = 0.427 (defined as T(*) = k(B)T/epsilon, where epsilon is the depth of the potential well). Interestingly, CNT has been found to overestimate the nucleation free energy barrier in 3D systems near the triple point. In fact, the agreement of the calculated nucleation rate with CNT is much worse in two dimensions than in three dimensions. The reason for the inadequacy of the CNT can be attributed to the noncircular nature of the critical clusters. Although the shape becomes increasingly circular and the clusters become more compact with increase in cutoff radius, an appreciable noncircular nature remains even without any cutoff to make the simple CNT inaccurate. PMID:19102549

  15. Nucleation of the diamond phase in aluminium-solid solutions

    NASA Technical Reports Server (NTRS)

    Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

    1993-01-01

    Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

  16. Nucleation and Growth of Gas Hydrate in Natural Seawater

    NASA Astrophysics Data System (ADS)

    Holman, S. A.; Osegovic, J. P.; Young, J. C.; Max, M. D.; Ames, A. L.

    2003-12-01

    Large-scale nucleation of gas hydrate takes place when hydrate-forming gas and seawater are brought together under suitable pressure-temperature conditions or where dissolved hydrate-forming gas in saturated or near-saturated seawater is chilled or brought to higher pressures. Profuse formation of hydrate shells on gas bubbles and nucleation of at least five different forms of gas hydrate have been achieved in fresh natural seawater. Growth of masses of solid gas hydrate takes place when hydrate-forming gas reactant dissolved in seawater is brought into the vicinity of the hydrate. The gas concentration of the enriched water in the vicinity of hydrate is higher than the hydrate equilibrium gas concentration. Hydrate growth under these conditions is accelerated due to the chemical potential difference between the enriched water and the hydrate crystals, which induces mass flux of dissolved hydrate forming gas into new hydrate crystals. As long as water enriched in the hydrate-forming gas is circulated into the vicinity of the hydrate, growth proceeds into the water space. Experimental approaches for growth of examples of solid masses of hydrate are presented. Results of these experiments provide an insight into the growth of gas hydrate under natural conditions where interstitial water in marine sediments is captured by burial from open seawater, and where solid gas hydrate forms on the seafloor. By using fresh natural seawater, which is a chemically and materially complex fluid, our experiments in pressurized, refrigerated reactors should closely track the growth history of solid hydrate in the natural environment. In our model for hydrate growth in sediments, nearly complete pore fill by diagenetic hydrate can best be accomplished by nucleation of hydrate at a point source within the pore water or at a particular point on sediment particulate, with growth outward into the water space that is refreshed with ground water having high concentrations of hydrate-forming gas. Best growth can be achieved by circulation of water through constricting pore space although dissolved gas will also migrate along diffusion gradients.

  17. Observing classical nucleation theory at work by monitoring phase transitions with molecular precision

    PubMed Central

    Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E.S.; Durán-Olivencia, Miguel A.; Maes, Dominique

    2014-01-01

    It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441

  18. Nucleation of a Non-Equilibrium Phase in a First Order Phase Transition; BCC ^4He from Superfluid

    NASA Astrophysics Data System (ADS)

    Johnson, T. A.; Elbaum, C.

    1996-03-01

    We report new observations of nucleation and phase transitions in superfluid helium four in which a metastable solid phase nucleates and grows from the overpressured liquid in preference to the stable phase. Ultimately, the stable phase nucleates from the superfluid independently and the metastable phase disappears. While the persistence of a phase in a metastable state is fairly common, the type of nucleation into a phase out of equilibrium described here does not appear to have been previously reported. We offer an account of these events in terms of interfacial free energy differences and resulting relative nucleation probabilities for different values of supercooling. Both classical and quantum mechanical evaluations of nucleation probabilities give qualitatively similar results.

  19. Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium.

    PubMed

    Martnez, Daniel M; Ferguson, Frank T; Heist, Richard H; Nuth, Joseph A

    2005-08-01

    In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate maximum. We then present and discuss the resulting nucleation onset supersaturation data within the context of nucleation theory based on the liquid droplet model. Nucleation results appear to be consistent with a cesium vapor-to-liquid nucleation study performed in a thermal diffusion cloud chamber. PMID:16108655

  20. Homogeneous and heterogeneous nucleations in the surface phase transition: Si(111)4 × 1-In

    NASA Astrophysics Data System (ADS)

    Shim, Hyungjoon; Jeon, Youjin; Yeo, Jonghoon; Lee, Geunseop

    2015-06-01

    Homogeneous and heterogeneous nucleations in a reduced-dimensional system undergoing a first-order structural phase transition were examined by using low electron energy diffraction and scanning tunneling microscopy. The high-temperature 4 × 1 phase of a Si(111)-In surface was supercooled at temperatures below the transition temperature ({T}{{c}}) and evolved slowly into a low-temperature 8 × 2 phase with time. The transition rate decreased significantly as the temperature approached {T}{{c}}. The kinetics of the observed homogeneous nucleation was analyzed by classical nucleation theory. The introduction of oxygen atoms reduced the hysteresis and accelerated nucleation significantly, showing that the {T}{{c}}-raising oxygen impurity plays the role of a nucleation seed for heterogeneous nucleation.

  1. Heat storage system comprising a phase change medium and a nucleating agent

    SciTech Connect

    Kai, J.; Kimura, H.

    1982-06-01

    A heat storage system comprises a phase change medium and a nucleating agent. The phase change medium is prepared by mixing a gest molecule and water if necessary, with a gelating agent, an emulsifier and/or a furan compound. The nucleating agent is filled in a capillary or a porous substrate.

  2. Measurements of Ice Nucleation in Arctic Mixed Phase Clouds

    NASA Astrophysics Data System (ADS)

    Brooks, S. D.; Glen, A.; Zelenyuk, A. N.; MacDonald, A. M.; Liu, P.; Leaitch, R.

    2008-12-01

    Here we present in-flight measurements of ice nuclei (IN) data collected with a Continuous Flow Diffusion Chamber (CFDC) from onboard the Canadian Convair during the recent Indirect and Semidirect Effects of Aerosol Campaign (ISDAC). During ISDAC, Arctic haze containing aerosols from several distinctly different sources including Asian dust and Siberia coal fire plants, were sampled. The corresponding range in aerosol-cloud interactions and overall influence of outside aerosol masses on the Arctic atmosphere was variable as well. During the project, ice nuclei were sampled in-cloud and out-of-cloud and in the presence of multiple distinct aerosol layers. The CFDC was operated at controlled temperatures in the range of -10 degrees C to -40 degrees C and over a wide range of supersaturations with respect to ice. Observed IN concentrations varied from frequent values of 0.01 per liter to spikes as high as approximately 10 per liter during Arctic haze events. The multiple factors contributing to this high degree of variability in ice nuclei will be discussed in an effort to determine what drives ice nucleation in mixed phase clouds in the Arctic.

  3. Heterogeneous Nucleation of the T1 Phase on Dispersoids in Al-Cu-Li Alloys

    NASA Astrophysics Data System (ADS)

    Tsivoulas, Dimitrios

    2015-06-01

    The major strengthening phase of modern Al-Cu-Li alloys, T1, is so far known to nucleate on a number of sites in the microstructure. However, its preferential nucleation on Al20Cu2Mn3 dispersoids has never been reported with strong evidence up to now. The present work suggests that such heterogeneous nucleation is possible and performs a comparison with the precipitates distributed homogeneously in the matrix. This phenomenon is shown to promote a particle decohesive fracture mode.

  4. Critical velocity for vortex nucleation in a finite-temperature Bose gas

    NASA Astrophysics Data System (ADS)

    Stagg, G. W.; Pattinson, R. W.; Barenghi, C. F.; Parker, N. G.

    2016-02-01

    We use classical field simulations of the homogeneous Bose gas to study the breakdown of superflow due to vortex nucleation past a cylindrical obstacle at finite temperature. Thermal fluctuations modify the vortex nucleation from the obstacle, turning antiparallel vortex lines (which would be nucleated at zero temperature) into wiggly lines, vortex rings, and even vortex tangles. We find that the critical velocity for vortex nucleation decreases with increasing temperature and scales with the speed of sound of the condensate, becoming zero at the critical temperature for condensation.

  5. Monte Carlo tests of nucleation concepts in the lattice gas model

    NASA Astrophysics Data System (ADS)

    Schmitz, Fabian; Virnau, Peter; Binder, Kurt

    2013-05-01

    The conventional theory of homogeneous and heterogeneous nucleation in a supersaturated vapor is tested by Monte Carlo simulations of the lattice gas (Ising) model with nearest-neighbor attractive interactions on the simple cubic lattice. The theory considers the nucleation process as a slow (quasistatic) cluster (droplet) growth over a free energy barrier ΔF*, constructed in terms of a balance of surface and bulk term of a critical droplet of radius R*, implying that the rates of droplet growth and shrinking essentially balance each other for droplet radius R=R*. For heterogeneous nucleation at surfaces, the barrier is reduced by a factor depending on the contact angle. Using the definition of physical clusters based on the Fortuin-Kasteleyn mapping, the time dependence of the cluster size distribution is studied for quenching experiments in the kinetic Ising model and the cluster size ℓ* where the cluster growth rate changes sign is estimated. These studies of nucleation kinetics are compared to studies where the relation between cluster size and supersaturation is estimated from equilibrium simulations of phase coexistence between droplet and vapor in the canonical ensemble. The chemical potential is estimated from a lattice version of the Widom particle insertion method. For large droplets it is shown that the physical clusters have a volume consistent with the estimates from the lever rule. Geometrical clusters (defined such that each site belonging to the cluster is occupied and has at least one occupied neighbor site) yield valid results only for temperatures less than 60% of the critical temperature, where the cluster shape is nonspherical. We show how the chemical potential can be used to numerically estimate ΔF* also for nonspherical cluster shapes.

  6. Monte Carlo tests of nucleation concepts in the lattice gas model.

    PubMed

    Schmitz, Fabian; Virnau, Peter; Binder, Kurt

    2013-05-01

    The conventional theory of homogeneous and heterogeneous nucleation in a supersaturated vapor is tested by Monte Carlo simulations of the lattice gas (Ising) model with nearest-neighbor attractive interactions on the simple cubic lattice. The theory considers the nucleation process as a slow (quasistatic) cluster (droplet) growth over a free energy barrier ΔF(*), constructed in terms of a balance of surface and bulk term of a critical droplet of radius R(*), implying that the rates of droplet growth and shrinking essentially balance each other for droplet radius R=R(*). For heterogeneous nucleation at surfaces, the barrier is reduced by a factor depending on the contact angle. Using the definition of physical clusters based on the Fortuin-Kasteleyn mapping, the time dependence of the cluster size distribution is studied for quenching experiments in the kinetic Ising model and the cluster size ℓ(*) where the cluster growth rate changes sign is estimated. These studies of nucleation kinetics are compared to studies where the relation between cluster size and supersaturation is estimated from equilibrium simulations of phase coexistence between droplet and vapor in the canonical ensemble. The chemical potential is estimated from a lattice version of the Widom particle insertion method. For large droplets it is shown that the physical clusters have a volume consistent with the estimates from the lever rule. Geometrical clusters (defined such that each site belonging to the cluster is occupied and has at least one occupied neighbor site) yield valid results only for temperatures less than 60% of the critical temperature, where the cluster shape is nonspherical. We show how the chemical potential can be used to numerically estimate ΔF(*) also for nonspherical cluster shapes. PMID:23767652

  7. Homogeneous nucleation rate measurements in 1-pentanol vapor with helium as a buffer gas

    NASA Astrophysics Data System (ADS)

    dmal, Vladimr.; Smolk, Ji?

    The rate of homogeneous nucleation in supersaturated vapors of n-pentanol was studied experimentally using an upward static diffusion chamber. Helium was used as a buffer gas, holding the total pressure in the chamber at Pt=25 kPa. A recently improved photographic technique was used to determine the nucleation rate as a function of supersaturation at temperature T=260 K. This dependence was compared with predictions made by the classical theory of homogeneous nucleation. Furthermore, the influence of gaseous ions on nucleation rate was studied, and a minimum voltage across the chamber, necessary to avoid nucleation on ions, was determined. The effect of the wall heating power on nucleation was found to be negligible in the range studied.

  8. Gas Phase Nanoparticle Synthesis

    NASA Astrophysics Data System (ADS)

    Granqvist, Claes; Kish, Laszlo; Marlow, William

    This book deals with gas-phase nanoparticle synthesis and is intended for researchers and research students in nanomaterials science and engineering, condensed matter physics and chemistry, and aerosol science. Gas-phase nanoparticle synthesis is instrumental to nanotechnology - a field in current focus that raises hopes for environmentally benign, resource-lean manufacturing. Nanoparticles can be produced by many physical, chemical, and even biological routes. Gas-phase synthesis is particularly interesting since one can achieve accurate manufacturing control and hence industrial viability.

  9. Heterogeneous nucleation of the primary phase in the rapid solidification of Al-4.5wt%Cu alloy droplet

    NASA Astrophysics Data System (ADS)

    Maitre, A.; Bogno, A.-A.; Bedel, M.; Reinhart, G.; Henein, H.

    2015-06-01

    This paper reports on rapid solidification of Al-Cu alloys. A heterogeneous nucleation/growth model coupled with a thermal model of a falling droplet through a stagnant gas was developed. The primary undercooling as well as the number of nucleation points was compared with Al-Cu alloy droplets produced by Impulse Atomization (IA). Based on experimental results from Neutron Diffraction, secondary (eutectic) phases were obtained. Then, primary and secondary undercoolings were estimated using the metastable extensions of solidus and liquidus lines calculated by Thermo-Calc. Moreover, Synchrotron X-ray microtomography has been performed on Al-4.5wt%Cu droplets. The undercoolings are in good agreement. Results also evidence the presence of one nucleation point and are in agreement with the experimental observations.

  10. Nucleation kinetics of polymorphic transition from phase II to phase III of hexachloroethane: Metastability/unstability

    NASA Astrophysics Data System (ADS)

    Koga, Yoshikata

    1987-10-01

    The conversions of the transition from phase II to III of C 2Cl 6 were measured for the range between 38.81 and 41.15°C (the transition point: 43.64°C). A simple model was devised appropriate to the present mononucleus transition. Using this, the induction periods, that are inversely proportional to the nucleation rates, were extracted from the observed curves. The resulting induction periods varied from 0.07 to 1500 h. In terms of the classical nucleation theory, though its applicability for such a wide variation is questionable, it was shown that there are two temperature regions bounded at about 40.8°C in which nucleation behaviours are different. As shown in the previous papers, the growth rates of the same transition were too fast to measure below a certain threshold temperature which was lower than 41.9°C. These threshold behaviours in nucleation and growth were tentatively attributed to the change-over from metastability to unstability.

  11. How Properties of Solid Surfaces Modulate the Nucleation of Gas Hydrate.

    PubMed

    Bai, Dongsheng; Chen, Guangjin; Zhang, Xianren; Sum, Amadeu K; Wang, Wenchuan

    2015-01-01

    Molecular dynamics simulations were performed for CO2 dissolved in water near silica surfaces to investigate how the hydrophilicity and crystallinity of solid surfaces modulate the local structure of adjacent molecules and the nucleation of CO2 hydrates. Our simulations reveal that the hydrophilicity of solid surfaces can change the local structure of water molecules and gas distribution near liquid-solid interfaces, and thus alter the mechanism and dynamics of gas hydrate nucleation. Interestingly, we find that hydrate nucleation tends to occur more easily on relatively less hydrophilic surfaces. Different from surface hydrophilicity, surface crystallinity shows a weak effect on the local structure of adjacent water molecules and on gas hydrate nucleation. At the initial stage of gas hydrate growth, however, the structuring of molecules induced by crystalline surfaces are more ordered than that induced by amorphous solid surfaces. PMID:26227239

  12. How Properties of Solid Surfaces Modulate the Nucleation of Gas Hydrate

    NASA Astrophysics Data System (ADS)

    Bai, Dongsheng; Chen, Guangjin; Zhang, Xianren; Sum, Amadeu K.; Wang, Wenchuan

    2015-07-01

    Molecular dynamics simulations were performed for CO2 dissolved in water near silica surfaces to investigate how the hydrophilicity and crystallinity of solid surfaces modulate the local structure of adjacent molecules and the nucleation of CO2 hydrates. Our simulations reveal that the hydrophilicity of solid surfaces can change the local structure of water molecules and gas distribution near liquid-solid interfaces, and thus alter the mechanism and dynamics of gas hydrate nucleation. Interestingly, we find that hydrate nucleation tends to occur more easily on relatively less hydrophilic surfaces. Different from surface hydrophilicity, surface crystallinity shows a weak effect on the local structure of adjacent water molecules and on gas hydrate nucleation. At the initial stage of gas hydrate growth, however, the structuring of molecules induced by crystalline surfaces are more ordered than that induced by amorphous solid surfaces.

  13. How Properties of Solid Surfaces Modulate the Nucleation of Gas Hydrate

    PubMed Central

    Bai, Dongsheng; Chen, Guangjin; Zhang, Xianren; Sum, Amadeu K.; Wang, Wenchuan

    2015-01-01

    Molecular dynamics simulations were performed for CO2 dissolved in water near silica surfaces to investigate how the hydrophilicity and crystallinity of solid surfaces modulate the local structure of adjacent molecules and the nucleation of CO2 hydrates. Our simulations reveal that the hydrophilicity of solid surfaces can change the local structure of water molecules and gas distribution near liquid-solid interfaces, and thus alter the mechanism and dynamics of gas hydrate nucleation. Interestingly, we find that hydrate nucleation tends to occur more easily on relatively less hydrophilic surfaces. Different from surface hydrophilicity, surface crystallinity shows a weak effect on the local structure of adjacent water molecules and on gas hydrate nucleation. At the initial stage of gas hydrate growth, however, the structuring of molecules induced by crystalline surfaces are more ordered than that induced by amorphous solid surfaces. PMID:26227239

  14. Correlated nucleation and self-accommodating kinetic pathway of ferroelectric phase transformation

    NASA Astrophysics Data System (ADS)

    Zhou, Jie E.; Cheng, Tian-Le; Wang, Yu U.

    2012-01-01

    Mechanisms of nucleation and growth of domains during ferroelectric phase transformation are investigated by using theoretical and computational approaches. It is shown that ferroelectric phase transformation exhibits some peculiar behaviors due to strong long-range dipole-dipole-like interactions involved in the system. Incorporation of electrostatic and elastostatic energies into the classical Landau-Ginzburg-Devonshire theory effectively modifies the coefficients of the polynomial free energy function and introduces extra energy barrier for ferroelectric phase transformation. It is found that independent nucleation of ferroelectric phase in the context of classical nucleation theory is prohibited, because electrostatic interaction generates an insurmountable energy barrier to isolated nucleus. Phase field modeling and computer simulation reveals that, in order to circumvent such an energy barrier, ferroelectric nucleation exhibits strong spatial correlation and self-organization behaviors from the very beginning, and ferroelectric phase transformation proceeds via spatial and temporal evolution of self-accommodating domains that provide a low-energy kinetic pathway throughout the phase transformation process. Theoretical analysis of the critical wavelength of correlated nucleation agrees with the computer simulation. Heterogeneous nucleation as induced by externally applied local electric field and subsequent polarization evolution process is also simulated to further demonstrate such self-organized pattern formation behaviors.

  15. Supercooling and transient phase induced nucleation in n-alkane solutions

    NASA Astrophysics Data System (ADS)

    Sirota, E. B.

    2000-01-01

    The supercooling exhibited by bulk solutions of the n-alkane tricosane (C23) in dodecane (C12) is measured as a function of concentration using adiabatic scanning calorimetry. For small dilutions where crystallization occurs into the rotator phase, negligible supercooling is observed. For larger dilutions where crystallization is into the herringbone crystal phase, nucleation occurs at the temperature where the rotator phase becomes stable with respect to the liquid. The supercooling in bulk n-alkane solutions is thus determined by the metastable phase diagram. This is a novel, but possibly often occurring mechanism where nucleation is induced by a transient metastable phase.

  16. Fluid phase thermodynamics : I) nucleate pool boiling of oxygen under magnetically enhanced gravity and II) superconducting cavity resonators for high-stability frequency references and precision density measurements of helium-4 gas

    NASA Astrophysics Data System (ADS)

    Corcovilos, Theodore Allen

    Although fluids are typically the first systems studied in undergraduate thermodynamics classes, we still have only a rudimentary phenomenological understanding of these systems outside of the classical and equilibrium regimes. Two experiments will be presented. First, we present progress on precise measurements of helium-4 gas at low temperatures (1 K-5 K). We study helium because at low densities it is an approximately ideal gas but at high densities the thermodynamic properties can be predicted by numerical solutions of Schroedinger's equation. By utilizing the high resolution and stability in frequency of a superconducting microwave cavity resonator we can measure the dielectric constant of helium-4 to parts in 109, corresponding to an equivalent resolution in density. These data will be used to calculate the virial coefficients of the helium gas so that we may compare with numerical predictions from the literature. Additionally, our data may allow us to measure Boltzmann's constant to parts in 108, a factor of 100 improvement over previous measurements. This work contains a description of the nearly-completed apparatus and the methods of operation and data analysis for this experiment. Data will be taken by future researchers.The second experiment discussed is a study of nucleate pool boiling. To date, no adequate quantitative model exists of this everyday phenomenon. In our experiment, we vary one parameter inaccessible to most researchers, gravity, by applying a magnetic force to our test fluid, oxygen. Using this technique, we may apply effective gravities of 0-80 times Earth's gravitational acceleration (g). In this work we present heat transfer data for the boiling of oxygen at one atmosphere ambient pressure for effective gravity values between 1g and 16g . Our data describe two relationships between applied heat flux and temperature differential: at low heat flux the system obeys a power law and at high heat flux the behavior is linear. We find that the transition heat flux between these two regimes scales as the 4th root of the gravitational acceleration, which may indicate a relationship to the critical heat flux. Additionally, we find that the low heat flux power law exponent is independent of gravity and the power law scale coefficient increases linearly with gravity.

  17. Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach

    NASA Astrophysics Data System (ADS)

    Pan, Weichun; Kolomeisky, Anatoly B.; Vekilov, Peter G.

    2005-05-01

    Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.

  18. Role of Dynamic Nucleation at Moving Boundaries in Phase and Microstructure Selection

    NASA Technical Reports Server (NTRS)

    Karma, Alain; Trivedi, Rohit

    1999-01-01

    Solidification microstructures that form under steady-state growth conditions (cells, dendrites, regular eutectics, etc.) are reasonably well understood in comparison to other, more complex microstructures, which form under intrinsically non-steady-state growth conditions due to the competition between the nucleation and growth of several phases. Some important practical examples in this latter class include microstructures forming in peritectic systems in highly undercooled droplets, and in strip cast stainless steels. Prediction of phase and microstructure selection in these systems has been traditionally based on (1) heterogeneous nucleation on a static interface, and (2) comparing the relative growth rate of different phase/microstructures under steady-state growth conditions. The formation of new phases, however, occurs via nucleation on, or ahead of, a moving boundary. In addition, the actual selection process is controlled by a complex interaction between the nucleation process and the growth competition between the nuclei and the pre-existing phase under non-steady-state conditions. As a result, it is often difficult to predict which microstructure will form and which phases will be selected under prescribed processing conditions. This research addresses this critical role of nucleation at moving boundaries in the selection of phases and solidification microstructures through quantitative experiments and numerical modeling in peritectic systems. In order to create a well characterized system in which to study this problem, we focus on the directional solidification of hypo- and hyper-peritectic alloys in the two-phase region, imposing a large enough ratio of temperature gradient/growth rate (G/V(sub p)) to suppress the morphological instability of both the parent (alpha) and peritectic (Beta) phases, i.e. each phase alone would grow as a planar front. Our combined experimental and theoretical results show that, already in this simplified case, the growth competition of these two phases leads to a rich variety of microstructures that depend sensitively upon the relative importance of nucleation, diffusion, and convection.

  19. Nucleation of atmospheric aerosol particles

    NASA Astrophysics Data System (ADS)

    Curtius, Joachim

    2006-11-01

    A significant fraction of the total number of particles present in the atmosphere is formed originally by nucleation from the gas phase. Binary nucleation of sulphuric acid and water, ternary nucleation of sulphuric acid, water and ammonia and ion-induced nucleation are thought to be the most important aerosol nucleation processes in the atmosphere. Within the last two decades, instrumentation to observe and characterize nucleation has improved greatly and numerous observations of nucleation have been made including quantification of the nucleation rate, characterization of the growth process and first chemical characterizations of the freshly formed particles. Nucleation has been observed at many different places in the atmosphere: in the boundary layer, in the free troposphere, in remote locations, in coastal areas, in boreal forests as well as urban areas and pollution plumes. In most cases gaseous sulphuric acid is assumed to be the key precursor gas. After nucleation, other supersaturated substances, especially low vapour pressure organics often take part in the subsequent aerosol growth. Iodine oxides seem to be responsible for nucleation observed in some coastal areas. Recent advances in modelling allow for a kinetic treatment of the nucleation process based on measured thermochemical data for the cluster formation. Considerable improvement over the classical nucleation treatment is expected from this approach. A detailed understanding of atmospheric aerosol nucleation processes is needed as the freshly formed particles directly influence the number concentration and size distribution of the atmospheric aerosol. The formation of clouds and precipitation is affected and influences on climate are anticipated. Anthropogenic emissions influence atmospheric aerosol nucleation processes considerably. Despite the comprehensive research efforts, substantial inconsistencies remain and conflicting results of laboratory studies, model studies as well as atmospheric observations persist. Several key questions about the predictability of atmospheric nucleation in general, about the substances, that take part in nucleation and subsequent growth and about the size and composition of the critical cluster, have not been resolved so far. To cite this article: J. Curtius, C. R. Physique 7 (2006).

  20. Micromechanical modeling of void nucleation in two phase materials

    NASA Astrophysics Data System (ADS)

    Shabrov, Maxim N.

    The present work consists of three parts. In the first part, void nucleation is studied both experimentally and computationally with the aim of identifying a macroscopic criterion for nucleation by particle cracking. Three types of circumferential notched cylindrical specimens made of a low alloy steel were used. The tensile tests were interrupted at various loads below the fracture load. The specimens were sectioned parallel to the loading axis and the locations of cracked and untracked titanium nitride inclusions were identified. Finite element calculations were carried out for each specimen geometry using conventional isotropic hardening plasticity theory. The ability of various potential void nucleation criteria to predict the onset of void nucleation by inclusion cracking is explored. In the second part, finite element analysis of the effect of particle fracture on the tensile response of particle-reinforced metal-matrix composites is carried out. The analysis is based on three-dimensional unit cell model. The reinforcement is characterized as an isotropic elastic solid and the ductile matrix as an isotropically hardening viscoplastic solid. An initial crack, perpendicular to the tensile axis, is assumed to be present in the particle. Quasi-statically growing cracks are analyzed. Resistance to crack growth in its initial plane and along the particle-matrix interface is modeled using a cohesive surface constitutive relation that allows decohesion. Variations of the size of initial crack present in the particle, particle morphology and stress state triaxiality are explored. Conditions governing the onset of cracking within the particle, the evolution of field quantities as the crack advances within the particle to the particle-matrix interface, and the dependence of overall tensile stress-strain response during continued crack advance are analyzed. In the third part, competition between particle cracking and debonding in metal-matrix composites is analyzed. The composite, containing a periodic array of particles, is represented in terms of a three-dimensional unit cell. The matrix is characterized as isotropically hardening elastic visco-plastic solid and the particle as an isotropic elastic solid. Particle cracking and debonding is modeled using cohesive zone framework. The effect of material and morphological properties on the competition between particle cracking and debonding is investigated.

  1. Role of Nucleation and Growth in Two-Phase Microstructure Formation

    SciTech Connect

    Jong Ho Shin

    2008-05-01

    During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (1) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (2) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

  2. Interplay between ?(Ti) nucleation and growth during peritectic solidification investigated by phase-field simulations.

    PubMed

    Eiken, J; Apel, M; Witusiewicz, V T; Zollinger, J; Hecht, U

    2009-11-18

    The properties of modern TiAl-based alloys with aluminum contents around 45at.% critically depend on the as solidified ?(Ti) grain structure. Commonly, a rather coarse grain structure is obtained if ?(Ti) forms via the peritectic reaction '[Formula: see text]'. Phase-field simulations have been applied to perform a case study of grain structure formation during the early peritectic growth under unidirectional growth conditions. In the absence of foreign nucleation sites, the peritectic ?(Ti) phase nucleates on the dendritic surface of the properitectic ?(Ti) phase. For typical values of the critical nucleation undercooling, coarse structures with large elongated grains are reproduced. A delicate interplay between nucleation and growth is predicted for reduced values of the critical undercooling. In this case, the alloy composition is found to play an additional role. An effective grain refinement by frequent nucleation is obtained, if potent nucleants can reduce the critical undercooling below the local growth undercooling. Complementary Scheil calculations and Bridgman experiments show that in situ precipitation of TiB(2) particles can be controlled by adequate boron addition. Both, numerical predictions and experiments confirm that these particles can act as effective nucleation agents and significantly reduce the grain size of ?(Ti). PMID:21715868

  3. Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Umo, N. S.; Murray, B. J.; Baeza-Romero, M. T.; Jones, J. M.; Lea-Langton, A. R.; Malkin, T. L.; O'Sullivan, D.; Plane, J. M. C.; Williams, A.

    2014-11-01

    Ice nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice nucleating particles, but the ice nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

  4. Competition of homogeneous and heterogeneous ice nucleation on secondary organic aerosol particles: The role of particle phase state

    NASA Astrophysics Data System (ADS)

    Berkemeier, Thomas; Shiraiwa, Manabu; Pschl, Ulrich; Koop, Thomas

    2014-05-01

    Recently, secondary organic aerosol (SOA) particles have been found to exhibit a highly viscous, amorphous state under atmospherically relevant conditions (Virtanen et al., 2010). Besides retardation of chemical reactions (Shiraiwa et al., 2011) and incomplete gas-to-particle partitioning of semi-volatile constituents (Vaden et al., 2011), these particles were found to suppress homogeneous ice nucleation (Murray et al., 2008), which normally takes place when a liquid particle reaches its respective homogeneous nucleation limit (Koop et al., 2000). In turn, glassy SOA particles may act themselves as heterogeneous ice nuclei as recent studies suggest (e.g. Murray et al., 2010, Wang et al., 2012). The predominant nucleation pathway for SOA particles is thus controlled by particle phase state. The phase state of SOA particles depends on several factors such as composition, temperature and relative humidity. In atmospheric updrafts, inducing a change in temperature and relative humidity, moisture- and temperature-induced phase transitions can occur (e.g. Shiraiwa et al., 2011). In fast updrafts, these particles may also deviate from humidification equilibrium, i.e. the agreement between ambient relative humidity and water activity inside the particle may not be established at any point in time. The extent of this temporal delay is governed by the updraft velocity, the particle size and the diffusivity of water inside the glassy organic particle matrix. Here we show how the delayed deliquescence of SOA particles can be quantified for SOA from a variety of precursors. A kinetic flux model (Shiraiwa et al., 2012) is applied and the predominant ice nucleation pathway is inferred from particle phase state at the respective homogeneous and heterogeneous nucleation limits. To estimate diffusivities inside the organic particle matrix for the relevant range of temperature and humidity, we developed a novel method that relies on glass transition and hygroscopic growth data that are more easily available. The model simulations suggest upper temperature boundaries, below which heterogeneous ice nucleation of glassy aerosols may occur, depending on updraft velocities and particle size. We also show that the predominant ice nucleation pathway depends on precursor material and oxidation state. References Koop, T. et al. (2000) Nature 406, 611. Murray, B. J. (2008) Atmos. Chem. Phys. 8, 5423. Murray, B. J. et al. (2010) Nature Geosci. 3, 233. Shiraiwa, M. et al. (2011) Proc. Natl. Acad. Sci. 108, 11003. Shiraiwa, M. et al. (2012) Atmos. Chem. Phys. 12, 2777. Virtanen, A. et al. (2010) Nature 467, 824. Vaden, T. D. et al. (2011) Proc. Natl. Acad. Sci., 108, 2190. Wang, B. et al. (2012) J. Geophys. Res., 117, D16209.

  5. Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.

    PubMed

    Carren-Caldern, Bernardo

    2012-10-14

    Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836

  6. Nonequilibrium thermodynamics of nucleation.

    PubMed

    Schweizer, M; Sagis, L M C

    2014-12-14

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects. PMID:25494727

  7. Nonequilibrium thermodynamics of nucleation

    NASA Astrophysics Data System (ADS)

    Schweizer, M.; Sagis, L. M. C.

    2014-12-01

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

  8. Nonequilibrium thermodynamics of nucleation

    SciTech Connect

    Schweizer, M.; Sagis, L. M. C.

    2014-12-14

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

  9. Homogeneous bubble nucleation in binary systems of liquid solvent and dissolved gas

    NASA Astrophysics Data System (ADS)

    Němec, Tomáš

    2016-03-01

    A formulation of the classical nucleation theory (CNT) is developed for bubble nucleation in a binary system composed of a liquid solvent and a dissolved gas. The theoretical predictions are compared to the experimental nucleation data of four binary mixtures, i.e. diethylether - nitrogen, propane - carbon dioxide, isobutane - carbon dioxide, and R22 (chlorodifluoromethane) - carbon dioxide. The presented CNT formulation is found to improve the precision of the simpler theoretical method of Ward et al. [J. Basic Eng. 92 (10), 71-80, 1970] based on the weak-solution approximation. By analyzing the available experimental nucleation data, an inconsistency in the data reported by Mori et al. [Int. J. Heat Mass Transfer, 19 (10), 1153-1159, 1976] for propane - carbon dioxide and R22 - carbon dioxide is identified.

  10. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition

    NASA Astrophysics Data System (ADS)

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V.; Stanley, H. Eugene; Reguera, David; Franzese, Giancarlo

    2015-06-01

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments

  11. Exploring the discrepancies between experiment, theory, and simulation for the homogeneous gas-to-liquid nucleation of 1-pentanol.

    PubMed

    Nellas, Ricky B; Keasler, Samuel J; Siepmann, J Ilja; Chen, Bin

    2010-04-28

    Using an efficient Monte Carlo approach known as Aggregation-Volume-bias Monte Carlo with self-adaptive Umbrella Sampling and Histogram Reweighting (AVUS-HR), we obtained the nucleation free energy profile of 1-pentanol at various temperatures from 220 to 360 K. From these profiles, differences between the free energy barrier heights obtained from our simulations and those predicted by the classical nucleation theory (CNT) were calculated. Our results strongly support that the logarithm of the nucleation rate ratio between simulation (or experiment) and CNT increases almost linearly with the inverse temperature. Among the various factors that contribute to the discrepancy between simulation and CNT nucleation rates, the nonzero surface free energy of the monomer included in the CNT makes the largest contribution. On the molecular level, the simulations indicate that a gas-phase cluster of 1-pentanol molecules is relatively compact and can contain multiple hydrogen bonded aggregates of various sizes and that this aggregate size distribution depends strongly on temperature and also on the overall size of the cluster system. PMID:20441298

  12. Collector phase transitions during vapor-solid-solid nucleation of GaN nanowires.

    PubMed

    Chze, Caroline; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver; Riechert, Henning

    2010-09-01

    We investigate the nucleation of Ni-induced GaN nanowires by in situ and ex situ experiments. Three nucleation stages are evidenced. In the first two stages, different crystal structures of the Ni collectors are identified. Real-time monitoring of the Ga desorption allows the amount of Ga incorporated in the collectors to be quantified. A transition of their crystal structure prior to nanowire growth is found to be in agreement with the thermodynamically stable phase sequence of the relevant phase diagrams. PMID:20715843

  13. Ice Nucleation in Mixed-Phase Clouds: Parameterization Evaluation and Climate Impacts

    NASA Astrophysics Data System (ADS)

    Liu, X.; Ghan, S. J.; Xie, S.; Boyle, J. S.; Klein, S. A.; Demott, P. J.; Prenni, A. J.

    2009-12-01

    There are still large uncertainties on ice nucleation mechanisms and ice crystal numbers in mixed-phase clouds, which affects modeled cloud phase, cloud lifetime and radiative properties in the Arctic clouds in global climate models. In this study we evaluate model simulations with three mixed-phase ice nucleation parameterizations (Phillips et al., 2008; DeMott et al., 2009; Meyers et al. 1992) against the Atmospheric Radiation Measurement (ARM) Indirect and Semi-Direct Aerosol Campaign (ISDAC) observations using the NCAR Community Atmospheric Model Version 4 (CAM4) running in the single column mode (SCAM) and in the CCPP-ARM Parameterization Testbed (CAPT) forecasts. It is found that SCAM and CAPT with the new physically-based ice nucleation schemes (Phillips et al., 2008; DeMott et al., 2009) produce a more realistic simulation of the cloud phase structure and the partitioning of condensed water into liquid droplets against observations during the ISDAC than the CAM with an oversimplified Meyers et al. (1992). Both SCAM simulations and CAPT forecasts suggest that the ice number concentration could play an important role in the simulated mixed-phase cloud microphysics, and thereby needs to be realistically represented in global climate models. The global climate implication of different ice nucleation parameterizations are also be studied.

  14. Aerosol formation by gas-phase-ozonolysis of small vinylethers

    NASA Astrophysics Data System (ADS)

    Sadezky, A.; Mellouki, A.; Winterhalter, R.; Rmpp, A.; Moortgat, G.

    2003-04-01

    Secondary organic aerosol (SOA) is formed in the troposphere by ozonolysis of biogenic VOC. The gas-phase processes however, which follow the ozonolysis reaction and lead to the formation of the nucleating compounds are so far poorly understood. A wide range of different primary or secondary products of gas-phase ozonolyses has so far been suggested as potential precursor of nucleation, such as secondary ozonides, dicarboxylic acids and their dimers, and peroxy compounds, such as peroxyhemiacetales or diacylperoxides. In order to assess the influences of oxygen groups in the neighborhood of the alkene double bond on reaction products and particle formation, gas-phase ozonolysis reactions of small vinylethers are investigated in this work. The observations might allow to draw conclusion on the likelihood of potential particle precursors to be formed in the gas phase and to have a sufficiently low vapour pressure for nucleation. Experiments have been carried out in a flow reactor of 1 m length in order to observe SOA formation during the first minute of the reaction, and in a 570 l spherical glass reactor in order to study nucleation or product formation dependent on the reaction time longer than 1 min. Particle size distributions are measured with a scanning mobility particle analyser (SMPS, Model 3936, TSI Inc.), product formation in the gas-phase is analysed by FTIR, and in the particle phase by LC-MS-MS. Threshold alkene conversions necessary for nucleation and initial particle formation are determined in the flow reactor by varying alkene concentrations at constant ozone concentrations and reaction times. Moreover, the influence of experimental conditions, such as relative humidity, is studied.

  15. Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Experimental evidence indicates a dominant role of solution phase interactions in nucleating and growing tetragonal lysozyme crystals. These interactions are extensive, even at saturation, and may be a primary cause of misoriented regions in crystals grown on Earth. Microgravity, by limiting interfacial concentrations to diffusion-controlled levels, may benefit crystal quality by also reducing the extent of associated species present at the interface.

  16. Homogeneous nucleation rate measurements of 1-propanol in helium: the effect of carrier gas pressure.

    PubMed

    Brus, David; Zdmal, Vladimr; Stratmann, Frank

    2006-04-28

    Kinetics of homogeneous nucleation in supersaturated vapor of 1-propanol was studied using an upward thermal diffusion cloud chamber. Helium was used as a noncondensable carrier gas and the influence of its pressure on observed nucleation rates was investigated. The isothermal nucleation rates were determined by a photographic method that is independent on any nucleation theory. In this method, the trajectories of growing droplets are recorded using a charge coupled device camera and the distribution of local nucleation rates is determined by image analysis. The nucleation rate measurements of 1-propanol were carried out at four isotherms 260, 270, 280, and 290 K. In addition, the pressure dependence was investigated on the isotherms 290 K (50, 120, and 180 kPa) and 280 K (50 and 120 kPa). The isotherm 270 K was measured at 25 kPa and the isotherm 260 K at 20 kPa. The experiments confirm the earlier observations from several thermal diffusion chamber investigations that the homogeneous nucleation rate of 1-propanol tends to increase with decreasing total pressure in the chamber. In order to reduce the possibility that the observed phenomenon is an experimental artifact, connected with the generally used one-dimensional description of transfer processes in the chamber, a recently developed two-dimensional model of coupled heat, mass, and momentum transfer inside the chamber was used and results of both models were compared. It can be concluded that the implementation of the two-dimensional model does not explain the observed effect. Furthermore the obtained results were compared both to the predictions of the classical theory and to the results of other investigators using different experimental devices. Plotting the experimental data on the so-called Hale plot shows that our data seem to be consistent both internally and also with the data of others. Using the nucleation theorem the critical cluster sizes were obtained from the slopes of the individual isotherms and compared with the Kelvin prediction. The influence of total pressure on the observed isothermal nucleation rate was studied in another experiment, where not only temperature but also supersaturation was kept constant as the total pressure was changed. It was shown that the dependence of the nucleation rate on pressure gets stronger as pressure decreases. PMID:16674134

  17. Nucleation-growth processes and isothermal kinetics of phase transformations in the methylhydrazine monohydrate

    NASA Astrophysics Data System (ADS)

    Lebrun, N.; Foulon, M.; Gors, C.; Ferriol, M.; Cohen-Adad, M. T.

    1997-07-01

    Phase transformations in the methylhydrazine monohydrate (CH 3NHNH 2 H 2O) are investigated by differential scanning calorimetry (DSC) over the temperature range 110-300 K. On cooling a glass is formed by quenching the liquid. Depending on the heating rate, two solid phases (metastable and/or stable) with slow phase transformation kinetics are observed. The optimal temperature for nucleation and growth processes have been determined for the two solid phases. The nucleation rate is maximum in the glass transition region ( Tg ? 160 K) and the temperature growth regions are, respectively, estimated to be 188-202 K for the metastable solid phase and 212-228 K for the stable solid phase. The metastable and the stable solid phases, respectively, melt at 220 and 234 K. The kinetic character of phase transitions is revealed by complementary X-ray measurements at 200 K. A phenomenological model based on Avrami's law is proposed for a better understanding of the growth mechanisms for the two solid phases. On reheating, the glassy state transforms to a metastable liquid. Then, a partial transformation (48%) into the metastable solid phase from this liquid begins at about 188 K. It is followed by the growth of the stable solid phase from the undercooled liquid and the metastable solid phase. The solid-solid transformation seems to be governed by contacts with the stable solid grains.

  18. Heterogeneous nucleation and growth dynamics in the light-induced phase transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Brady, Nathaniel F.; Appavoo, Kannatassen; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit P.; Haglund, Richard F., Jr.; Hilton, David J.

    2016-03-01

    We report on ultrafast optical investigations of the light-induced insulator-to-metal phase transition in vanadium dioxide with controlled disorder generated by substrate mismatch. These results reveal common dynamics of this optically-induced phase transition that are independent of this disorder. Above the fluence threshold for completing the transition to the rutile crystalline phase, we find a common time scale, independent of sample morphology, of 40.5+/- 2 ps that is consistent with nucleation and growth dynamics of the R phase from the parent M1 ground state.

  19. Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses

    SciTech Connect

    Pavlov, Konstantin M.; Paganin, David M.; Vine, David J.; Schmalz, Jelena A.; Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto; Jakubek, Jan; Altissimo, Matteo; Clark, Jesse N.

    2011-01-15

    Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

  20. Heterogeneous nucleation and growth dynamics in the light-induced phase transition in vanadium dioxide.

    PubMed

    Brady, Nathaniel F; Appavoo, Kannatassen; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit P; Haglund, Richard F; Hilton, David J

    2016-03-31

    We report on ultrafast optical investigations of the light-induced insulator-to-metal phase transition in vanadium dioxide with controlled disorder generated by substrate mismatch. These results reveal common dynamics of this optically-induced phase transition that are independent of this disorder. Above the fluence threshold for completing the transition to the rutile crystalline phase, we find a common time scale, independent of sample morphology, of [Formula: see text] ps that is consistent with nucleation and growth dynamics of the R phase from the parent M1 ground state. PMID:26932975

  1. Ice nucleation through immersion freezing in mixed-phase stratiform clouds: Theory and numerical simulations

    NASA Astrophysics Data System (ADS)

    de Boer, Gijs; Hashino, Tempei; Tripoli, Gregory J.

    2010-05-01

    Mixed-phase stratiform cloud layers have commonly been observed at several Arctic locations. However, mechanisms governing production of ice in these cloud layers remain poorly understood. Because of this, models have difficulties correctly representing a steady-state mixed-phase stratus layer. Based on recent lidar and radar measurements of these clouds, along with measurements of Arctic aerosols, the idea of an active immersion freezing regime is presented. This nucleation mechanism provides a pathway for limited production of ice within a super cooled liquid layer, and avoids rapid glaciation through the Bergeron-Findeissen process. The nucleation theory and supporting observations and simulations are presented, along with a discussion of implications of results on future simulation and understanding of mixed-phase stratus.

  2. Nucleation of (He-3)-B from the A phase - A cosmic-ray effect?

    NASA Technical Reports Server (NTRS)

    Leggett, A. J.

    1984-01-01

    When He-3 is liquified and subsequently cooled, it undergoes, at a temperature of approximately 2.0-2.5 mK, a second-order transition into the so-called A phase. On further cooling, a first-order transition occurs, and the liquid passes into the B phase. Supercooling occurs with respect to the second transition, and the problem of nucleation arises. In connection with the experimental interest in studying metastable (He-3)-A down to the lowest temperatures in weak magnetic fields, the understanding of the mechanism of this transition and the feasibility of its inhibition is of some importance. The present investigation is concerned with the possibility that the transition is nucleated by the passage of a cosmic ray through the sample cell.

  3. Phase-field modelling for metals and colloids and nucleation therein-an overview.

    PubMed

    Emmerich, H

    2009-11-18

    Phase-field modelling, as it is understood today, is still a young discipline in condensed matter physics, which established itself for that class of systems in condensed matter physics, which can be characterized by domains of different phases separated by a distinct interface. Driven out of equilibrium, their dynamics results in the evolution of those interfaces, during which those might develop into well-defined structures with characteristic length scales at the nano-, micro-or mesoscale. Since the material properties of such systems are, to a large extent, determined by those small-scale structures, acquiring a precise understanding of the mechanisms that drive the interfacial dynamics is a great challenge for scientists in this field. Phase-field modelling is an approach that allows us to tackle this challenge simulation-based. This overview summarizes briefly the essentials of the conceptual background of the phase-field method, as well as recent issues the phase-field community is focusing on, as far as they are related to nucleation. To that end a brief introduction to the basic understanding underlying the diffuse interface description, which is the conceptual backbone of phase-field modelling, is given at the beginning, followed by a detailed picture of its achievements so far in applications to nucleation phenomena in metals and colloids. Within the most relevant fields of condensed matter physics, approached by phase-field modelling until now, applications to metallic systems are a traditional domain of phase-field modelling and nucleation phenomena therein have been addressed by several groups. This paper provides an overview of these. Advances in the field of colloidal systems, on the other hand, are only more recent and are addressed here in the context of contributions to soft matter physics in general. PMID:21715867

  4. Bubble nucleation in first-order inflation and other cosmological phase transitions

    SciTech Connect

    Turner, M.S. Departments of Physics and Astronomy Astrophysics, Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637-1433 ); Weinberg, E.J. Department of Physics, Columbia University, New York, New York 10027 School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 ); Widrow, L.M. )

    1992-09-15

    We address in some detail the kinematics of bubble nucleation and percolation in first-order cosmological phase transitions, with the primary focus on first-order inflation. We study how a first-order phase transition completes, describe measures of its progress, and compute the distribution of bubble sizes. For example, we find that the typical bubble size in a successful transition is of order 1% to 100% of the Hubble radius, and depends very weakly on the energy scale of the transition. We derive very general conditions that must be satisfied by {Gamma}/{ital H}{sup 4} to complete the phase transition ({Gamma}=bubble nucleation rate per unit volume; {ital H}=expansion rate; physically, {Gamma}/{ital H}{sup 4} corresponds to the volume fraction of space occupied by bubbles nucleated over a Hubble time). In particular, {Gamma}/{ital H}{sup 4} must exceed 9/4{pi} to successfully end inflation. To avoid the deleterious effects of bubbles nucleated early during inflation on primordial nucleosynthesis and on the isotropy and spectrum of the cosmic microwave background radiation, during most of inflation {Gamma}/{ital H}{sup 4} must be less than order 10{sup {minus}4}--10{sup {minus}3}. Our constraints imply that in a successful model of first-order inflation the phase transition must complete over a period of at most a few Hubble times and all but preclude individual bubbles from providing an interesting source of density perturbation. We note, though, that it is just possible for Poisson fluctuations in the number of moderately large-size bubbles to lead to interesting isocurvature perturbations, whose spectrum is not scale invariant. Finally, we analyze in detail several recently proposed models of first-order inflation.

  5. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition.

    PubMed

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V; Stanley, H Eugene; Reguera, David; Franzese, Giancarlo

    2015-01-01

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments. PMID:26095898

  6. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition

    PubMed Central

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V.; Stanley, H. Eugene; Reguera, David; Franzese, Giancarlo

    2015-01-01

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments PMID:26095898

  7. The Gas Nucleation Process Study of Anatase TiO2 in Atmospheric Non-Thermal Plasma Enhanced Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Wu, Maoshui; Xu, Yu; Dai, Linjun; Wang, Tiantian; Li, Xue; Wang, Dexin; Guo, Ying; Ding, Ke; Huang, Xiaojiang; Shi, Jianjun; Zhang, Jing

    2014-01-01

    The gas phase nucleation process of anatase TiO2 in atmospheric non-thermal plasma enhanced chemical vapor deposition is studied. The particles synthesized in the plasma gas phase at different power density were collected outside of the reactor. The structure of the collected particles has been investigated by field scanning electron microscope (FESEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The analysis shows that uniform crystalline nuclei with average size of several nanometers have been formed in the scale of micro second through this reactive atmospheric plasma gas process. The crystallinity of the nanoparticles increases with power density. The high density of crystalline nanonuclei in the plasma gas phase and the low gas temperature are beneficial to the fast deposition of the 3D porous anatase TiO2 film.

  8. Underbarrier nucleation kinetics in a metastable quantum liquid near the liquid-gas spinodal line

    SciTech Connect

    Burmistrov, S.N.; Dubovskii, L.B.; Okuda, Y.

    2005-02-01

    We develop a theory that incorporates the relaxation properties of a condensed medium into the quantum decay of a metastable liquid near the liquid-gas spinodal line at low temperatures. We find that both the regime and the rate of quantum nucleation strongly depend on the relaxation time and its temperature behavior. The quantum nucleation rate slows down with decreasing relaxation time. We also discuss the low-temperature experiments on cavitation in normal {sup 3}He and superfluid {sup 4}He at negative pressures. It is the drastic distinctions in the properties of the high-frequency sound mode and in the temperature behavior of the relaxation time that make the quantum cavitation kinetics in {sup 3}He and {sup 4}He completely different.

  9. Microphysical Consequences of the Spatial Distribution of Ice Nucleation in Mixed-Phase Stratiform Clouds

    SciTech Connect

    Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

    2014-07-28

    Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation, leads to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. [2013]. The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud-volume, cloud-top, and cloud-base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from ISDAC, a lower bound of 0.006 m^3/s is obtained for the ice crystal formation rate.

  10. The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

    PubMed

    Hyvrinen, Antti-Pekka; Brus, David; Zdmal, Vladimr; Smolk, Jiri; Kulmala, Markku; Viisanen, Yrj; Lihavainen, Heikki

    2006-06-14

    Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons. PMID:16784271

  11. Gas-phase chemical dynamics

    SciTech Connect

    Weston, R.E. Jr.; Sears, T.J.; Preses, J.M.

    1993-12-01

    Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

  12. Report on the Implementation of Homogeneous Nucleation Scheme in MARMOT-based Phase Field Simulation

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin

    2013-09-30

    In this report, we summarized our effort in developing mesoscale phase field models for predicting precipitation kinetics in alloys during thermal aging and/or under irradiation in nuclear reactors. The first part focused on developing a method to predict the thermodynamic properties of critical nuclei such as the sizes and concentration profiles of critical nuclei, and nucleation barrier. These properties are crucial for quantitative simulations of precipitate evolution kinetics with phase field models. Fe-Cr alloy was chosen as a model alloy because it has valid thermodynamic and kinetic data as well as it is an important structural material in nuclear reactors. A constrained shrinking dimer dynamics (CSDD) method was developed to search for the energy minimum path during nucleation. With the method we are able to predict the concentration profiles of the critical nuclei of Cr-rich precipitates and nucleation energy barriers. Simulations showed that Cr concentration distribution in the critical nucleus strongly depends on the overall Cr concentration as well as temperature. The Cr concentration inside the critical nucleus is much smaller than the equilibrium concentration calculated by the equilibrium phase diagram. This implies that a non-classical nucleation theory should be used to deal with the nucleation of Cr precipitates in Fe-Cr alloys. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. A number of interesting phenomena were observed from the simulations: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrated that it is critical to introduce the correct critical nuclei into phase field modeling in order to correctly capture the kinetics of precipitation. In most alloys the matrix phase and precipitate phase have different concentrations as well as different crystal structures. For example, Cu precipitates in FeCu alloys have fcc crystal structure while the matrix Fe-Cu solid solution has bcc structure at low temperature. The WBM model and KimS model, where both concentrations and order parameters are chosen to describe the microstructures, are commonly used to model precipitations in such alloys. The WBM and KimS models have not been implemented into Marmot yet. In the second part of this report, we focused on implementing the WBM and KimS models into Marmot. The Fe-Cu alloys, which are important structure materials in nuclear reactors, was taken as the model alloys to test the models.

  13. Nanoscale Phase Stability Reversal During the Nucleation and Growth of Titanium Oxide Minerals

    NASA Astrophysics Data System (ADS)

    Hummmer, D. R.; Heaney, P. J.; Kubicki, J. D.; Kent, P. R.; Post, J. E.

    2008-12-01

    Fine-grained titanium oxide minerals are important in soils, where they affect a variety of geochemical processes. They are also industrially important as catalysts, pigments, food additives, and dielectrics. Recent research has indicated an apparent reversal of thermodynamic stability between TiO2 phases at the nanoscale thought to be caused by an increased contribution of surface energy to the total free energy. Time-resolved X-ray diffraction (XRD) experiments in which titanium oxides crystallize from aqueous TiCl4 solutions confirm that anatase, a metastable phase, is always the first phase to nucleate under our range of initial conditions. Rutile peaks are observed only minutes after the first appearance of anatase, after which anatase abundance slowly decreases while rutile continues to form. Whole pattern refinement of diffraction data reveals that lattice constants of both phases increase throughout the crystallization process. In addition, transmission electron microscope (TEM) observations and kinetic modeling indicate that anatase does not undergo a solid-state transformation to the rutile structure as once thought. Instead, anatase appears to re-dissolve and then feed the growth of already nucleated rutile nanocrystals. Density functional theory (DFT) calculations were employed to model 1, 2, and 3 nm particles of both mineral phases. The total surface energies calculated from these models did yield lower values for anatase than for rutile by 8-13 kJ/mol depending on particle size, indicating that surface free energy is sufficient to account for stability reversal. However, these whole-particle surface energies were much higher than the sum of energies of each particle's constituent crystallographic surfaces. We attribute the excess energy to defects associated with the edges and corners of nanoparticles, which are not present on a 2-D periodic surface. This previously unreported edge and corner energy may play a dominant role in the stability reversal of nanocrystalline titanium oxides, as well as other mineral systems susceptible to reversals in phase stability at the nanoscale.

  14. Detached Melt Nucleation during Diffusion Brazing of a Technical Ni-based Superalloy: A Phase-Field Study

    NASA Astrophysics Data System (ADS)

    Böttger, B.; Apel, M.; Laux, B.; Piegert, S.

    2015-06-01

    Advanced solidification processes like welding, soldering, and brazing are often characterized by their specific solidification conditions. But they also may include different types of melting processes which themselves are strongly influenced by the initial microstructures and compositions of the applied materials and therefore are decisive for the final quality and mechanical properties of the joint. Such melting processes are often not well- understood because - compared to other fields of solidification science - relatively little research has been done on melting by now. Also, regarding microstructure simulation, melting has been strongly neglected in the past, although this process is substantially different from solidification due to the reversed diffusivities of the involved phases. In this paper we present phase-field simulations showing melting, solidification and precipitation of intermetallic phases during diffusion brazing of directionally solidified and heat-treated high-alloyed Ni- based gas turbine blade material using different boron containing braze alloys. Contrary to the common belief, melting of the base material is not always planar and can be further accompanied by detached nucleation and growth of a second liquid phase inside the base material leading to polycrystalline morphologies of the joint after solidification. These findings are consistent with results from brazed laboratory samples, which were characterized by EDX and optical microscopy, and can be explained in terms of specific alloy thermodynamics and inter-diffusion kinetics. Consequences of the gained new understanding for brazing of high- alloyed materials are discussed.

  15. Aerosol Inflluence on Ice Nucleation via the Immersion Mode in Mixed-Phase Arctic Stratiform Clouds

    NASA Astrophysics Data System (ADS)

    de Boer, G.; Hashino, T.; Tripoli, G. J.; Eloranta, E. W.

    2009-12-01

    Mixed-phase stratiform clouds are commonly observed at high latitudes (e.g. Shupe et al., 2006; de Boer et al., 2009a). Herman and Goody (1976), as well as Curry et al. (1996) present summaries of Arctic cloud climatologies that show low altitude stratus frequencies of up to 70% during transitional seasons. In addition to their frequent occurrence, these clouds have significant impacts on the near-surface atmospheric radiative budget, with estimates of wintertime reductions in net surface cooling of 40-50 Wm-2 (Curry et al., 1996) due predominantly to liquid in the mixed-phase layer. Both observational and modeling studies (e.g. Harrington et al., 1999; Jiang et al., 2000; Shupe et al., 2008; Klein et al., 2008) show a strong connection between the amount of ice present and the lifetime of the liquid portion of the cloud layer. This is thought to occur via the Bergeron-Findeissen mechanism (Pruppacher and Klett, 1997) in which ice grows at the expense of liquid due to its lower saturation vapor pressure. Unfortunately, the mechanisms by which ice is nucleated within these mixed-phase layers are not yet fully understood, and therefore an accurate depiction of this process for mixed-phase stratiform clouds has not yet been characterized. The nucleation mechanisms that are active in a given environment are sensitive to aerosol properties. Insoluble particles are typically good nuclei for ice particle formation, while soluble particles are typically better at nucleating water droplets. Aerosol observations from the Arctic often show mixed aerosol particles that feature both soluble and insoluble mass (Leaitch et al., 1984). Soluble mass fractions for these particles have been shown to be high, with estimates of 60-80% and are often made up of sulfates (Zhou et al., 2001; Bigg and Leck, 2001). It is believed that a significant portion of this sulfate mass comes from dimethyl sulfide (DMS) production in the Arctic Ocean and subsequent atmospheric oxidation. Since these mixed particles may initially nucleate liquid droplets that then contain the remaining insoluble mass, immersion freezing has been theorized to contribute to ice nucleation in these clouds (de Boer et al., 2009b). In this work, we present a numerical study focusing on immersion freezing in mixed-phase stratiform clouds. We investigate the effects of aerosol properties such as soluble mass fraction, insoluble mass type and aerosol concentration on cloud liquid water fraction and lifetime. The high-resolution simulations used are based on the current GEWEX Cloud System Study (GCSS)/World Meteorological Organization (WMO) mixed-phase stratus model intercomparison (Morrison and Zuidema, 2008) and are completed using the University of Wisconsin Non-Hydrostatic Modeling System (UW-NMS, Tripoli, 1992) in combination with an advanced bin microphysical scheme (AMPS, Hashino and Tripoli, 2008). Immersion freezing is represented using a parameterization from Diehl and Wurzler (2004), which accounts for the freezing point depression due to the concentration of soluble mass within the water droplet.

  16. The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds.

    PubMed

    Atkinson, James D; Murray, Benjamin J; Woodhouse, Matthew T; Whale, Thomas F; Baustian, Kelly J; Carslaw, Kenneth S; Dobbie, Steven; O'Sullivan, Daniel; Malkin, Tamsin L

    2013-06-20

    The amount of ice present in mixed-phase clouds, which contain both supercooled liquid water droplets and ice particles, affects cloud extent, lifetime, particle size and radiative properties. The freezing of cloud droplets can be catalysed by the presence of aerosol particles known as ice nuclei. One of the most important ice nuclei is thought to be mineral dust aerosol from arid regions. It is generally assumed that clay minerals, which contribute approximately two-thirds of the dust mass, dominate ice nucleation by mineral dust, and many experimental studies have therefore focused on these materials. Here we use an established droplet-freezing technique to show that feldspar minerals dominate ice nucleation by mineral dusts under mixed-phase cloud conditions, despite feldspar being a minor component of dust emitted from arid regions. We also find that clay minerals are relatively unimportant ice nuclei. Our results from a global aerosol model study suggest that feldspar ice nuclei are globally distributed and that feldspar particles may account for a large proportion of the ice nuclei in Earth's atmosphere that contribute to freezing at temperatures below about -15?C. PMID:23760484

  17. Phase-field simulation of irradiated metals Part II : Gas bubble kinetics.

    SciTech Connect

    Millett, P. C.; El-Azab, A.; Wolf, D.

    2011-01-01

    The phase-field model developed in Part I of this work is expanded to include fission gas generation, diffusion, and segregation within bubbles nucleated both homogeneously and heterogeneously along grain boundaries. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of the irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy and bubble density are investigated.

  18. Observing in space and time the ephemeral nucleation of liquid-to-crystal phase transitions

    NASA Astrophysics Data System (ADS)

    Yoo, Byung-Kuk; Kwon, Oh-Hoon; Liu, Haihua; Tang, Jau; Zewail, Ahmed H.

    2015-10-01

    The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at different times provide the structural transformation and the specific degree of crystallinity (?) in the evolution process. It is found that the temporal behaviour of ? exhibits unique `two-step' dynamics, with a robust `plateau' that extends over a microsecond; the rate constants vary by two orders of magnitude. Such behaviour reflects the presence of intermediate structure(s) that are the precursor of the ordered crystal state. Theoretically, we extend the well-known Johnson-Mehl-Avrami-Kolmogorov equation, which describes the isothermal process with a stretched-exponential function, but here over the range of times covering the melt-to-crystal transformation.

  19. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

  20. Microphysical consequences of the spatial distribution of ice nucleation in mixed-phase stratiform clouds

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

    2014-07-01

    Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation lead to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. (2013). The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud volume, cloud top, and cloud base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from Indirect and Semi-Direct Aerosol Campaign, a lower bound of 0.006 m-3 s-1 is obtained for the ice crystal formation rate.

  1. Thin interface analysis of a phase-field model for epitaxial growth with nucleation and Ehrlich-Schwoebel effects

    NASA Astrophysics Data System (ADS)

    Dong, X. L.; Xing, H.; Chen, C. L.; Luo, B. C.; Chen, Z.; Zhang, R. L.; Jin, K. X.

    2014-11-01

    In this paper, we perform thin interface analysis of a quantitative phase field model for epitaxial growth where nucleation and the Ehrlich-Schwoebel barrier have been considered. Results show that once the nucleation term is introduced into the phase-field model, modification must be carried out to get rid of the extrinsic “kinetic nucleation effect”. While in the ES effect, the asymmetric diffusivity accounts for an irrational step motion that leads the model to deviate from the sharp-interface approximation, hence another modification for the attachment time should be carried. Attributed to these modifications, the phase-field model is more quantitative in describing step flow dynamics in the sharp-interface limit, as well as exhibiting the more convergence of the steady-state velocity with respect to the step width for larger scale simulations. Our analysis and modifications explore the quantitative linking between atom motions and step dynamics.

  2. Inherent structures of phase-separating binary mixtures: Nucleation, spinodal decomposition, and pattern formation

    NASA Astrophysics Data System (ADS)

    Sarkar, Sarmistha; Bagchi, Biman

    2011-03-01

    An energy landscape view of phase separation and nonideality in binary mixtures is developed by exploring their potential energy landscape (PEL) as functions of temperature and composition. We employ molecular dynamics simulations to study a model that promotes structure breaking in the solute-solvent parent binary liquid, at low temperatures. The PEL of the system captures the potential energy distribution of the inherent structures (IS) of the system and is obtained by removing the kinetic energy (including that of intermolecular vibrations). The broader distribution of the inherent structure energy for structure breaking liquid than that of the structure making liquid demonstrates the larger role of entropy in stabilizing the parent liquid of the structure breaking type of binary mixtures. At high temperature, although the parent structure of the structure breaking binary mixture is homogenous, the corresponding inherent structure is found to be always phase separated, with a density pattern that exhibits marked correlation with the energy of its inherent structure. Over a broad range of intermediate inherent structure energy, bicontinuous phase separation prevails with interpenetrating stripes as signatures of spinodal decomposition. At low inherent structure energy, the structure is largely phase separated with one interface where as at high inherent structure energy we find nucleation type growth. Interestingly, at low temperature, the average inherent structure energy () exhibits a drop with temperature which signals the onset of crystallization in one of the phases while the other remains in the liquid state. The nonideal composition dependence of viscosity is anticorrelated with average inherent structure energy.

  3. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.

    2003-01-01

    From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.

  4. An anisotropic phase-field crystal model for heterogeneous nucleation of ellipsoidal colloids

    NASA Astrophysics Data System (ADS)

    Prieler, R.; Hubert, J.; Li, D.; Verleye, B.; Haberkern, R.; Emmerich, H.

    2009-11-01

    We derive a generalized model for isotropic as well as anisotropic crystal lattice systems of arbitrary Poisson ratio within the framework of the continuum phase-field crystal (PFC) approach (Elder and Grant 2004 Phys. Rev. E 70 051606). To this end we extend the simplest PFC model defined by a free energy functional, which is based upon the Swift-Hohenberg model of pattern formation (Swift and Hohenberg 1993 Phys. Rev. A 15 851) to a conservative, anisotropic Langevin equation. By studying heterogeneous nucleation of ellipsoidal colloids at a wall, we demonstrate the capacity of our approach to contribute to the more precise understanding of condensed matter systems built up from non-spherical units at the atomic scale. In particular we address the question of how (a) the orientation of the ellipsoids as well as (b) the interaction potential with the wall determine the resulting contact angle.

  5. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation Behavior of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.

    2003-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si[3], for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

  6. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.; Holland-Moritz, D.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si(3), for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron X-ray and high flux neutron facilities.

  7. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Curreri, Peter A. (Technical Monitor); Kelton, K. F.; Gangopadhyay, A.; Lee, G. W.; Hyers, R. W.; Rathz, R. J.; Rogers, J.; Schenk, T.; Simonet, V.; Holland-Moritz, D.

    2003-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si, for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

  8. Ice nucleation by different types of soil dusts under mixed-phase cloud conditions: Laboratory studies and atmospheric implications

    NASA Astrophysics Data System (ADS)

    Tobo, Y.; DeMott, P. J.; Hill, T. C. J.; Prenni, A. J.; Swoboda-Colberg, N. G.; Franc, G. D.; Kreidenweis, S. M.

    2014-12-01

    It has been suggested that ice nucleation by desert soil dusts composed largely of minerals plays an important role in forming ice crystals in mixed-phase clouds and subsequent precipitation. More recently, several studies have suggested that soil dusts having higher contents of soil organic matter (SOM) may also contribute significantly to atmospheric ice nucleation. In this study, we examine the ice nucleation properties of soil dusts derived from different locations in the world. Our results show that the ice nucleating ability of agricultural soil dusts derived from the largest dust source regions in North America is almost comparable to that of desert soil dusts at temperatures colder than about -15C. We also confirm that the agricultural soil dusts can serve as effective ice nuclei (IN) at much warmer temperatures. On the other hand, our results indicate that the ice nucleating ability of the agricultural soil dusts is significantly reduced after H2O2 digestion, while the reduction is not significant for the desert soil dusts. In this regard, based on single particle analysis, we demonstrate that such a significant reduction observed in the agricultural soil dusts is mainly attributable to the removal of organic-rich particles (namely, SOM particles), which have much higher ice nucleating ability than mineral particles. Moreover, we discuss the potential contributions of these soil dusts to atmospheric IN populations.

  9. An Effective Continuum Model for the Liquid-to-Gas Phase Change in a Porous Medium Driven by Solute Diffusion: II. Constant Liquid Withdrawal Rates

    SciTech Connect

    Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.

    2001-08-15

    This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.

  10. Kinetics of ion-induced nucleation in a vapor-gas mixture.

    PubMed

    Fisenko, Sergey P; Kane, David B; El-Shall, M Samy

    2005-09-01

    A general solution for the steady-state ion-induced nucleation kinetics has been derived, considering the differences between ion-induced nucleation and homogeneous nucleation. This solution includes a new effect for nucleation kinetics, the interaction of charged clusters with vapor molecules. Analytical expressions for the ion-induced nucleation rate have been obtained for the limiting cases of high and low thermodynamic barriers. The physical explanation of the so-called sign effect is proposed based on multipole expansion of an electric field of the cluster ion. This theory gives good agreement with experiments and is used to elucidate experimentally observed phenomena. PMID:16178615

  11. Inclusion phases and the nucleation of acicular ferrite in submerged arc welds in high strength low alloy steels

    NASA Astrophysics Data System (ADS)

    Dowling, J. M.; Corbett, J. M.; Kerr, H. W.

    1986-09-01

    Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained many different compounds, the proportions of each depending upon both the flux and metallic additions. Six inclusion phases have been identified: galaxite (Al2O3 ? MnO), a titanium-rich compound (probably TiO), a copper sulfide, a manganese sulfide, a silica, and an aluminum-rich phase. No correlation was found between the amount of acicular ferrite in the weld metal and either average inclusion composition or individual inclusion phases. No epitaxial relationships between inclusions and adjacent ferrite grains could be identified. It has been concluded that inclusions nucleate acicular ferrite by acting as inert substrates according to the classical theory of heterogeneous nucleation. Because most inclusions are multi-phase and are touched by several ferrite grains, it has also been concluded that each inclusion can nucleate several ferrite grains, due to local regions of high surface energy on the inclusion.

  12. Experimental studies on nucleation, nanoparticle's formation and polymerization from the vapor phase

    NASA Astrophysics Data System (ADS)

    Abdelsayed, Victor Maher

    This research is divided into three major parts. In part I, the critical supersaturations required for the homogeneous nucleation of 2,2,2-trifluorothanol (TFE) vapor have been measured over a temperature range (266-296 K) using an upward thermal diffusion cloud chamber (DCC). The measured supersaturations are in agreement with the predictions of both the classical and the scaled theory of nucleation. Moreover, the condensation of supersaturated TFE vapor on laser-vaporized magnesium nanoparticles has been studied under different experimental conditions, such as the supersaturation, the pressure and the electric field. In part II, the laser vaporization controlled condensation (LVCC) technique was used to prepare Au-Ag alloy nanoparticles in the vapor phase using designed targets of compressed Au and Ag micron-sized powder mixtures of selected composition. The results showed that the optical properties of these nanoparticles could be tuned depending on the alloy composition and the laser wavelength. Different intermetallic nanoparticles (FeAl and NiAl) from the vapor phase has also been prepared, using the same approach. In this work, the fraction of the charged particles generated during the laser vaporization process was used to prepare a new class of nanoparticle assemblies in the LVCC chamber under the influence of an electric field. The results showed that the electric field required to induce the formation of these nanoassemblies is material and field dependent. By coupling the LVCC chamber with the differential mobility analyzer, size-selected nanoparticles have been prepared in the vapor phase. The prepared nanoparticles were characterized by different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectroscopy. In part III, new methods were developed to prepare nanoparticle-polymer composites from the vapor phase. In the first method, the LVCC method was used to prepare a carbonaceous cross-linked resin, with different nanoparticles (Ni, Pt and FeAl) embedded inside. In the second method, free radical-thermally initiated polymerization was used to polymerize a monomer vapor of styrene on the surfaces of activated Ni nanoparticles.

  13. Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.

    PubMed

    Tth, Gyula I; Tegze, Gyrgy; Pusztai, Tams; Tth, Gergely; Grnsy, Lszl

    2010-09-15

    We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517

  14. Observing in space and time the ephemeral nucleation of liquid-to-crystal phase transitions.

    PubMed

    Yoo, Byung-Kuk; Kwon, Oh-Hoon; Liu, Haihua; Tang, Jau; Zewail, Ahmed H

    2015-01-01

    The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at different times provide the structural transformation and the specific degree of crystallinity (?) in the evolution process. It is found that the temporal behaviour of ? exhibits unique 'two-step' dynamics, with a robust 'plateau' that extends over a microsecond; the rate constants vary by two orders of magnitude. Such behaviour reflects the presence of intermediate structure(s) that are the precursor of the ordered crystal state. Theoretically, we extend the well-known Johnson-Mehl-Avrami-Kolmogorov equation, which describes the isothermal process with a stretched-exponential function, but here over the range of times covering the melt-to-crystal transformation. PMID:26478194

  15. Observing in space and time the ephemeral nucleation of liquid-to-crystal phase transitions

    PubMed Central

    Yoo, Byung-Kuk; Kwon, Oh-Hoon; Liu, Haihua; Tang, Jau; Zewail, Ahmed H.

    2015-01-01

    The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at different times provide the structural transformation and the specific degree of crystallinity (η) in the evolution process. It is found that the temporal behaviour of η exhibits unique ‘two-step' dynamics, with a robust ‘plateau' that extends over a microsecond; the rate constants vary by two orders of magnitude. Such behaviour reflects the presence of intermediate structure(s) that are the precursor of the ordered crystal state. Theoretically, we extend the well-known Johnson–Mehl–Avrami–Kolmogorov equation, which describes the isothermal process with a stretched-exponential function, but here over the range of times covering the melt-to-crystal transformation. PMID:26478194

  16. Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.

    2001-01-01

    Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

  17. Formation of Large Chiral Domains in the B4 Phase by Nucleation and Chirality-Preserving Growth of Helical Filaments

    NASA Astrophysics Data System (ADS)

    Chen, D.; Glaser, M. A.; Maclennan, J. E.; Clark, N. A.; Korblova, E.; Walba, D. M.

    2010-03-01

    The growth of helical filaments in the B4 phase is investigated in mixtures of a bent-core mesogen (NOBOW) and a calamitic mesogen (8CB). Due to freezing point depression, the B4 phase forms directly from isotropic phase in the mixtures. This enables us to show, for the first time, that the left- and right- chiral domains are composed of left- and right- handed helical filaments respectively. The formation of a chiral domain can be described as a nucleation and growth process, starting from a nucleus of arbitrary chirality. Starting from such a nucleus, the local chirality is maintained by chirality-preserving growth of helical filaments. The formation of large chiral domains in the mixture is due to the low density of nucleation sites. A tree branching model of the B4 helical filament growth has been proposed which accounts for the observed local homochirality of the helical filaments and the local phase coherence between the helical filaments.

  18. Reduced sediment melting at 7.5-12 GPa: phase relations, geochemical signals and diamond nucleation

    NASA Astrophysics Data System (ADS)

    Brey, G. P.; Girnis, A. V.; Bulatov, V. K.; Höfer, H. E.; Gerdes, A.; Woodland, A. B.

    2015-08-01

    Melting of carbonated sediment in the presence of graphite or diamond was experimentally investigated at 7.5-12 GPa and 800-1600 °C in a multianvil apparatus. Two starting materials similar to GLOSS of Plank and Langmuir (Chem Geol 145:325-394, 1998) were prepared from oxides, carbonates, hydroxides and graphite. One mixture (Na-gloss) was identical in major element composition to GLOSS, and the other was poorer in Na and richer in K (K-gloss). Both starting mixtures contained ~6 wt% CO2 and 7 wt% H2O and were doped at a ~100 ppm level with a number of trace elements, including REE, LILE and HFSE. The near-solidus mineral assemblage contained a silica polymorph (coesite or stishovite), garnet, kyanite, clinopyroxene, carbonates (aragonite and magnesite-siderite solid solution), zircon, rutile, bearthite and hydrous phases (phengite and lawsonite at <9 GPa and the hydrous aluminosilicates topaz-OH and phase egg at >10 GPa). Hydrous phases disappear at ~900 °C, and carbonates persist up to 1000-1100 °C. At temperatures >1200 °C, the mineral assemblage consists of coesite or stishovite, kyanite and garnet. Clinopyroxene stability depends strongly on the Na content in the starting mixture; it remains in the Na-gloss composition up to 1600 °C at 12 GPa, but was not observed in K-gloss experiments above 1200 °C. The composition of melt or fluid changes gradually with increasing temperature from hydrous carbonate-rich (<10 wt% SiO2) at 800-1000 °C to volatile-rich silicate liquids (up to 40 wt% SiO2) at high temperatures. Trace elements were analyzed in melts and crystalline phases by LA ICP MS. The garnet-melt and clinopyroxene-melt partition coefficients are in general consistent with results from the literature for volatile-free systems and silicocarbonate melts derived by melting carbonated peridotites. Most trace elements are strongly incompatible in kyanite and silica polymorphs ( D < 0.01), except for V, Cr and Ni, which are slightly compatible in kyanite ( D > 1). Aragonite and Fe-Mg carbonate have very different REE partition coefficients ( D Mst-Sd/L ~ 0.01 and D Arg/L ~ 1). Nb, Ta, Zr and Hf are strongly incompatible in both carbonates. The bearthite/melt partition coefficients are very high for LREE (>10) and decrease to ~1 for HREE. All HFSE are strongly incompatible in bearthite. In contrast, Ta, Nb, Zr and Hf are moderately to strongly compatible in ZrSiO4 and TiO2 phases. Based on the obtained partition coefficients, the composition of a mobile phase derived by sediment melting in deep subduction zones was calculated. This phase is strongly enriched in incompatible elements and displays a pronounced negative Ta-Nb anomaly but no Zr-Hf anomaly. Although all experiments were conducted in the diamond stability field, only graphite was observed in low-temperature experiments. Spontaneous diamond nucleation and the complete transformation of graphite to diamond were observed at temperatures above 1200-1300 °C. We speculate that the observed character of graphite-diamond transformation is controlled by relationships between the kinetics of metastable graphite dissolution and diamond nucleation in a hydrous silicocarbonate melt that is oversaturated in C.

  19. PHASE-FIELD SIMULATION OF IRRADIATED METALS: PART II: GAS BUBBLE KINETICS

    SciTech Connect

    Paul C Millett; Anter El-Azab

    2011-01-01

    We present a phase-field model for inert gas bubble formation and evolution in irradiated metals. The model evolves vacancy, self-interstitial, and fission gas atoms through a coupled set of Cahn-Hilliard and Allen-Cahn equations, capturing the processes of defect generation, recombination, annihilation at GB sinks, as well as intragranular and intergranular bubble nucleation and growth in polycrystalline microstructures. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of varying irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy on GB motion, and bubble density are investigated.

  20. Phase-field simulations of gas density within bubbles under irradiation

    SciTech Connect

    Paul C. Millett; Anter El-Azab; Michael Tonks

    2011-05-01

    Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles. In our simulations, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid regions. We find that gas densities within bubbles fluctuate drastically in the early nucleation stages, when growth rates are highest, but converge to steady-state values during the later coarsening stages. The steady-state gas densities within bubbles correspond with the ratio of total accumulated vacancy content divided by the total accumulated gas content, in agreement with a thermodynamic analysis concerning free-energy minimization.

  1. Vapourtoliquid nucleation: Nucleation theorems for nonisothermalnonideal case

    SciTech Connect

    Malila, J.; McGraw, R.; Napari, I.; Laaksonen, A.

    2010-08-29

    Homogeneous vapour-to-liquid nucleation, a basic process of aerosol formation, is often considered as a type example of nucleation phenomena, while most treatment of the subject introduce several simplifying assumptions (ideal gas phase, incompressible nucleus, isothermal kinetics, size-independent surface free energy...). During last decades, nucleation theorems have provided new insights into properties of critical nuclei facilitating direct comparison between laboratory experiments and molecular simulations. These theorems are, despite of their generality, often applied in forms where the aforementioned assumptions are made. Here we present forms of nucleation theorems that explicitly take into account these effects and allow direct estimation of their importance. Only assumptions are Arrhenius-type kinetics of nucleation process and exclusion carrier gas molecules from the critical nucleus.

  2. A model for phase change kinetics in polymer composites with significant fiber surface nucleation

    SciTech Connect

    Benard, A.

    1998-09-18

    A model for the isothermal crystallization of fiber-reinforced polymers with significant nucleation on the fibers is presented. The model is based on exact and approximate expressions for the volume of intersection between a cylinder and a sphere located on the outside radius of the cylinder which allows to account for the effects of the fibers on the overall crystallization process. The crystallization process is divided into time frames according to the validity of the solutions for the volume of intersection. The evolution of the crystallinity is computed for both thermal and athermal nucleation processes. The accelerating effect of fiber-nucleated spherulites on the overall crystallization process is demonstrated with simple examples in which parameters such as the fiber volume fraction, the fiber radius, the nucleation density and an induction time are changed. Limitations of the current model are also discussed.

  3. Effects of the cosmological expansion on the bubble nucleation rate for relativistic first-order phase transitions

    SciTech Connect

    Metaxas, Dimitrios

    2008-09-15

    I calculate the first corrections to the dynamical preexponential factor of the bubble nucleation rate for a relativistic first-order phase transition in an expanding cosmological background by estimating the effects of the Hubble expansion rate on the critical bubbles of Langer's statistical theory of metastability. I also comment on possible applications and problems that arise when one considers the field theoretical extensions of these results (the Coleman-De Luccia and Hawking-Moss instantons and decay rates)

  4. Free-energy landscape and nucleation pathway of polymorphic minerals from solution in a Potts lattice-gas model.

    PubMed

    Okamoto, Atsushi; Kuwatani, Tatsu; Omori, Toshiaki; Hukushima, Koji

    2015-10-01

    Metastable minerals commonly form during reactions between water and rock. The nucleation mechanism of polymorphic phases from solution are explored here using a two-dimensional Potts model. The model system is composed of a solvent and three polymorphic solid phases. The local state and position of the solid phase are updated by Metropolis dynamics. Below the critical temperature, a large cluster of the least stable solid phase initially forms in the solution before transitioning into more-stable phases following the Ostwald step rule. The free-energy landscape as a function of the modal abundance of each solid phase clearly reveals that before cluster formation, the least stable phase has an energetic advantage because of its low interfacial energy with the solution, and after cluster formation, phase transformation occurs along the valley of the free-energy landscape, which contains several minima for the regions of three phases. Our results indicate that the solid-solid and solid-liquid interfacial energy contribute to the formation of the complex free-energy landscape and nucleation pathways following the Ostwald step rule. PMID:26565191

  5. Free-energy landscape and nucleation pathway of polymorphic minerals from solution in a Potts lattice-gas model

    NASA Astrophysics Data System (ADS)

    Okamoto, Atsushi; Kuwatani, Tatsu; Omori, Toshiaki; Hukushima, Koji

    2015-10-01

    Metastable minerals commonly form during reactions between water and rock. The nucleation mechanism of polymorphic phases from solution are explored here using a two-dimensional Potts model. The model system is composed of a solvent and three polymorphic solid phases. The local state and position of the solid phase are updated by Metropolis dynamics. Below the critical temperature, a large cluster of the least stable solid phase initially forms in the solution before transitioning into more-stable phases following the Ostwald step rule. The free-energy landscape as a function of the modal abundance of each solid phase clearly reveals that before cluster formation, the least stable phase has an energetic advantage because of its low interfacial energy with the solution, and after cluster formation, phase transformation occurs along the valley of the free-energy landscape, which contains several minima for the regions of three phases. Our results indicate that the solid-solid and solid-liquid interfacial energy contribute to the formation of the complex free-energy landscape and nucleation pathways following the Ostwald step rule.

  6. The effects of hygroscopicity on ice nucleation of fossil fuel combustion aerosols in mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Yun, Y.; Penner, J. E.; Popovicheva, O.

    2013-04-01

    Fossil fuel black carbon and organic matter (ffBC/OM) are often emitted together with sulfate, which coats the surface of these particles and changes their hygroscopicity. Observational studies at cirrus temperatures (?-40 C) show that the hygroscopicity of soot particles can modulate their ice nucleation ability. Here, we implement a scheme for 3 categories of soot (hydrophobic, hydrophilic and hygroscopic) on the basis of laboratory data and specify their ability to act as ice nuclei at mixed-phase temperatures by extrapolating the observations using a published deposition/condensation/immersion freezing parameterization. The new scheme results in significant changes to anthropogenic forcing in mixed-phase clouds. The net forcing in our offline model studies varies from 0.111 to 1.059 W m-2 depending on the ice nucleation capability of hygroscopic soot particles. The total anthropogenic cloud forcing and whole-sky forcing with the new scheme are 0.06 W m-2 and -2.45 W m-2, respectively, but could be more positive (by about 1.17 W m-2) if hygroscopic soot particles are allowed to nucleate ice particles. The change in liquid water path dominates the anthropogenic forcing in mixed-phase clouds.

  7. Rate processes in gas phase

    NASA Technical Reports Server (NTRS)

    Hansen, C. F.

    1983-01-01

    Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

  8. Nucleation mechanism of nano-sized NaZn13-type and ?-(Fe,Si) phases in La-Fe-Si alloys during rapid solidification.

    PubMed

    Hou, Xue-Ling; Xue, Yun; Liu, Chun-Yu; Xu, Hui; Han, Ning; Ma, Chun-Wei; Phan, Manh-Huong

    2015-01-01

    The nucleation mechanism involving rapid solidification of undercooled La-Fe-Si melts has been studied experimentally and theoretically. The classical nucleation theory-based simulations show a competitive nucleation process between the ?-(Fe,Si) phase (size approximately 10 to 30nm) and the cubic NaZn13-type phase (hereinafter 1:13 phase, size approximately 200 to 400nm) during rapid solidification, and that the undercooled temperature change ?T plays an important factor in this process. The simulated results about the nucleation rates of the ?-(Fe,Si) and 1:13 phases in La-Fe-Si ribbons fabricated by a melt-spinner using a copper wheel with a surface speed of 35m/s agree well with the XRD, SEM, and TEM studies of the phase structure and microstructure of the ribbons. Our study paves the way for designing novel La-Fe-Si materials for a wide range of technological applications. PMID:25852432

  9. Transient nucleation in glasses

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.

    1991-01-01

    Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

  10. Gas-phase magnetohydrodynamic disk accelerator

    NASA Astrophysics Data System (ADS)

    Pozdnyakov, G. A.

    2007-06-01

    A pulsed gas-phase magnetohydrodynamic (MHD) disk accelerator with a radial initial gas flow and radial electric current direction is described. Some working regime parameters and characteristics of the accelerated natural gas flow are reported. MHD accelerators of this type can be used for the investigation of chemical kinetics. Another promising application is related to the development of supersonic gas-phase endothermal chemical reactors with gasdynamic control.

  11. Phase field models for heterogeneous nucleation: Application to inoculation in alpha-solidifying Ti-Al-B alloys

    NASA Astrophysics Data System (ADS)

    Apel, M.; Eiken, J.; Hecht, U.

    2014-02-01

    This paper aims at briefly reviewing phase field models applied to the simulation of heterogeneous nucleation and subsequent growth, with special emphasis on grain refinement by inoculation. The spherical cap and free growth model (e.g. A.L. Greer, et al., Acta Mater. 48, 2823 (2000)) has proven its applicability for different metallic systems, e.g. Al or Mg based alloys, by computing the grain refinement effect achieved by inoculation of the melt with inert seeding particles. However, recent experiments with peritectic Ti-Al-B alloys revealed that the grain refinement by TiB2 is less effective than predicted by the model. Phase field simulations can be applied to validate the approximations of the spherical cap and free growth model, e.g. by computing explicitly the latent heat release associated with different nucleation and growth scenarios. Here, simulation results for point-shaped nucleation, as well as for partially and completely wetted plate-like seed particles will be discussed with respect to recalescence and impact on grain refinement. It will be shown that particularly for large seeding particles (up to 30 ?m), the free growth morphology clearly deviates from the assumed spherical cap and the initial growth - until the free growth barrier is reached - significantly contributes to the latent heat release and determines the recalescence temperature.

  12. Finite-Size Effects on Liquid-Solid Phase Coexistence and the Estimation of Crystal Nucleation Barriers

    NASA Astrophysics Data System (ADS)

    Statt, Antonia; Virnau, Peter; Binder, Kurt

    2015-01-01

    A fluid in equilibrium in a finite volume V with particle number N at a density ? =N /V exceeding the onset density ?f of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

  13. A Refined Approach to Bubble Nucleation and Polymer Foaming Process: Dissolved Gas and Cluster Size Effects

    PubMed

    Lee; Flumerfelt

    1996-12-25

    A refined approach to bubble nucleation is presented and applied to polymer foaming process. The integral overall energy balance and the integral Clausius-Duhem inequality are used to analyze a bubble nucleation experiment. The computation of long-range intermolecular potential results in expressions for surface tension, work, and critical work for cluster formation, as functions of the Hamaker constant, molecular and/or repeat unit interaction distance, molar fractions of each component, and cluster radius. The variation of surface tension with cluster size, temperature, and pressure is determined in terms of well-known macroscopic properties and compared with available experimental data. PMID:8978536

  14. Gas phase kinetics during normal combustion

    NASA Technical Reports Server (NTRS)

    Price, C. F.; Boggs, T. L.; Eisel, J. L.; Atwood, A. I.; Zurn, D. E.

    1980-01-01

    The role of gas phase kinetics during combustion was explored in the steady state modeling efforts and in the analysis of ignition phenomena. In both cases it was shown that the combustion characteristics of some high energy ingredients and propellants are strongly affected, if not dictated, by the gas phase reactions which take place.

  15. Unprecedented gas-phase chiroselective logic gates.

    PubMed

    Botta, Bruno; Fraschetti, Caterina; D'Acquarica, Ilaria; Sacco, Fabiola; Mattay, Jochen; Letzel, Matthias C; Speranza, Maurizio

    2011-03-21

    The gas-phase encounters between 2-aminobutane and proton-bound chiral resorcin[4]arene/nucleoside complexes behave in the gas phase as supramolecular "chiroselective logic gates" by releasing the nucleoside depending on the resorcin[4]arene and the 2-aminobutane configurations. PMID:21279226

  16. On the nucleation mechanism of the ?-? phase transition in the energetic nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine

    NASA Astrophysics Data System (ADS)

    Smilowitz, L.; Henson, B. F.; Greenfield, M.; Sas, A.; Asay, B. W.; Dickson, P. M.

    2004-09-01

    In our previous work on the mechanism for the ?-? solid-solid phase transition in octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), we used an empirical mechanism for the nucleation step and hypothesized a defect mechanism that was greatly affected by the presence of a nitroplasticizer/estane binder in the HMX formulation. Since then, we have acquired further evidence for this and have separated out the components of the binder to confirm that it is the nitroplasticizer that controls the nucleation energy in HMX formulations containing a nitroplasticizer/estane binder. While the exact distribution of nucleation energies as a function of synthesis route/defect type has not been worked out, it is likely that the solubility of the HMX in the nitroplasticizer is responsible for lowering the nucleation energy at the crystal surface, and therefore determines the nucleation rate for the formulation.

  17. Nucleation of lamellar domains from a sponge phase under shear flow: Shape selection of nuclei in a nonequilibrium steady state.

    PubMed

    Miyazawa, Hideyuki; Tanaka, Hajime

    2007-07-01

    It is a fundamental physical problem how a state is selected in a nonequilibrium steady state where the energy is continuously dissipated. This problem is common to phase transitions in liquids under shear flow and those in solids under deformation or electric current. In particular, soft matter often exhibits a strong nonlinear response to an external field, since its structural susceptibility to the external field is extremely large due to its softness and flexibility. Here we study the nucleation and growth process of the lamellar phase from the sponge phase under shear flow in a bilayer-forming surfactant system. We found an interesting shape selection of lamellar nuclei under shear flow between multilamellar vesicles (onions) and cylinders (leeks). These two types of behavior are separated sharply at a critical shear rate: a slight change of the shear rate is enough to switch one behavior to the other. We also found that, under a sufficiently strong shear flow, nucleated onions decrease their size with time, and eventually transform into leeks. This suggests that leeks may be the stable morphology under steady shear flow. However, the stability is limited only to the lamellar-sponge coexistence region. When a system enters into the lamellar phase region by further cooling, leeks lose their stability and break up into rather monodisperse onions, presumably via Rayleigh-like instability of a fluid tube. On the basis of these results, we draw a dynamic state diagram of smectic membrane organization under shear flow. PMID:17677456

  18. The homogeneous nucleation of 1-pentanol in a laminar flow diffusion chamber: The effect of pressure and kind of carrier gas

    NASA Astrophysics Data System (ADS)

    Brus, D.; Hyvrinen, A.-P.; Wedekind, J.; Viisanen, Y.; Kulmala, M.; dmal, V.; Smolk, J.; Lihavainen, H.

    2008-04-01

    The influence of total pressure and kind of carrier gas on homogeneous nucleation rates of 1-pentanol was investigated using experimental method of laminar flow diffusion chamber in this study. Two different carrier gases (helium and argon) were used in the total pressure range from 50to400kPa. Nucleation temperatures ranged from 265to290K for 1-pentanol-helium and from 265to285K for 1-pentanol-argon. Nucleation rates varied between 101 and 106cm-3s-1 for 1-pentanol-helium and between 102 and 105cm-3s-1 for 1-pentanol-argon. Both positive and slight negative pressure effects were observed depending on temperature and carrier gas. The trend of pressure effect was found similar for both carrier gases. Error analysis on thermodynamic properties was conducted, and the lowering of surface tension due to adsorption of argon on nucleated droplets was estimated. A quantitative overview of pressure effect is provided.

  19. Microstructual path analysis of polycrystalline solidification by using multi-phase-field method incorporating a nucleation model

    NASA Astrophysics Data System (ADS)

    Nishida, Yasutaka; Aiga, Fumihiko; Itoh, Satoshi

    2014-11-01

    Using the multi-phase-field (MPF) method incorporating a continuous nucleation model, we have revisited polycrystalline solidification described by the KJMA kinetics. Besides the Avrami exponents, the microstructural path functions to quantify the morphological characteristics were calculated within the framework of the MPF method. Our simulation can easily take account of the effects that are difficult to deduce from the conventional KJMA theory such as grain impingement and spatial distribution of crystallite seeds. As a result, quantitative differences among various types of transformation kinetics can be identified.

  20. Thermodynamics and kinetics of binary nucleation in ideal-gas mixtures.

    PubMed

    Alekseechkin, Nikolay V

    2015-08-01

    The nonisothermal single-component theory of droplet nucleation [N. V. Alekseechkin, Physica A 412, 186 (2014)] is extended to binary case; the droplet volume V, composition x, and temperature T are the variables of the theory. An approach based on macroscopic kinetics (in contrast to the standard microscopic model of nucleation operating with the probabilities of monomer attachment and detachment) is developed for the droplet evolution and results in the derived droplet motion equations in the space (V, x, T)—equations for V̇≡dV/dt, ẋ, and Ṫ. The work W(V, x, T) of the droplet formation is obtained in the vicinity of the saddle point as a quadratic form with diagonal matrix. Also, the problem of generalizing the single-component Kelvin equation for the equilibrium vapor pressure to binary case is solved; it is presented here as a problem of integrability of a Pfaffian equation. The equation for Ṫ is shown to be the first law of thermodynamics for the droplet, which is a consequence of Onsager's reciprocal relations and the linked-fluxes concept. As an example of ideal solution for demonstrative numerical calculations, the o-xylene-m-xylene system is employed. Both nonisothermal and enrichment effects are shown to exist; the mean steady-state overheat of droplets and their mean steady-state enrichment are calculated with the help of the 3D distribution function. Some qualitative peculiarities of the nucleation thermodynamics and kinetics in the water-sulfuric acid system are considered in the model of regular solution. It is shown that there is a small kinetic parameter in the theory due to the small amount of the acid in the vapor and, as a consequence, the nucleation process is isothermal. PMID:26254656

  1. Thermodynamics and kinetics of binary nucleation in ideal-gas mixtures

    NASA Astrophysics Data System (ADS)

    Alekseechkin, Nikolay V.

    2015-08-01

    The nonisothermal single-component theory of droplet nucleation [N. V. Alekseechkin, Physica A 412, 186 (2014)] is extended to binary case; the droplet volume V, composition x, and temperature T are the variables of the theory. An approach based on macroscopic kinetics (in contrast to the standard microscopic model of nucleation operating with the probabilities of monomer attachment and detachment) is developed for the droplet evolution and results in the derived droplet motion equations in the space (V, x, T)—equations for V ˙ ≡ d V / d t , x ˙ , and T ˙ . The work W(V, x, T) of the droplet formation is obtained in the vicinity of the saddle point as a quadratic form with diagonal matrix. Also, the problem of generalizing the single-component Kelvin equation for the equilibrium vapor pressure to binary case is solved; it is presented here as a problem of integrability of a Pfaffian equation. The equation for T ˙ is shown to be the first law of thermodynamics for the droplet, which is a consequence of Onsager's reciprocal relations and the linked-fluxes concept. As an example of ideal solution for demonstrative numerical calculations, the o-xylene-m-xylene system is employed. Both nonisothermal and enrichment effects are shown to exist; the mean steady-state overheat of droplets and their mean steady-state enrichment are calculated with the help of the 3D distribution function. Some qualitative peculiarities of the nucleation thermodynamics and kinetics in the water-sulfuric acid system are considered in the model of regular solution. It is shown that there is a small kinetic parameter in the theory due to the small amount of the acid in the vapor and, as a consequence, the nucleation process is isothermal.

  2. Phase-field Modeling of Gas Bubbles and Thermal Conductivity Evolution in Nuclear Fuels

    SciTech Connect

    Hu, Shenyang Y.; Henager, Charles H.; Heinisch, Howard L.; Stan, Marius; Baskes, Michael I.; Valone, Steven

    2009-07-15

    The major factors that influence the thermal conductivity of the ceramics and metals are temperature, stoichiometry, microstructure, porosity, and point defects. Nuclear fuels and structure materials are subject to a severe radiation environment and their properties, including thermal conductivity change significantly with time and irradiation level. In particular, the accumulation of fission products and the formation of He bubbles can decrease the heat transfer, leading to overheating of the fuel element. In this work, we use the phase-field method to study the effect of microstructural changes on thermal conductivity. We developed a phase-field model to simulate the He bubble formation and growth in a single/polycrystalline material with defects. The model takes into account the generation of gas atoms and defects, gas atom diffusivity inhomogeneity, gas atom segregation, and gas bubble nucleation. With the model, we simulated the gas bubble and temperature evolution, and calculated the effect of gas bubble volume fraction on effective thermal conductivity.

  3. Analyses of movement and contact of two nucleated cells using a gas-driven micropipette aspiration technique.

    PubMed

    Yang, Hao; Tong, Chunfang; Fu, Changliang; Xu, Yanhong; Liu, Xiaofeng; Chen, Qin; Zhang, Yan; L, Shouqin; Li, Ning; Long, Mian

    2016-01-01

    Adhesion between two nucleated cells undergoes specific significances in immune responses and tumor metastasis since cellular adhesive molecules usually express on two apposed cell membranes. However, quantification of the interactions between two nucleated cells is still challenging in microvasculature. Here distinct cell systems were used, including three types of human cells (Jurkat cell or PMN vs. MDA-MB-231 cell) and two kinds of murine native cells (PMN vs. liver sinusoidal endothelial cell). Cell movement, compression to, and relaxation from the counterpart cell were quantified using an in-house developed gas-driven micropipette aspiration technique (GDMAT). This assay is robust to quantify this process since cell movement and contact inside a pipette are independent of the repeated test cycles. Measured approaching or retraction velocity follows well a normal distribution, which is independent on the cycle period. Contact area or duration also fits a Gaussian distribution and moreover contact duration is linearly correlated with the cycle period. Cell movement is positively related to gas flux but negatively associated to medium viscosity. Cell adhesion tends to reach an equilibrium state with increase of cycle period or contact duration. These results further the understanding in the dynamics of cell movement and contact in microvasculature. PMID:26631492

  4. Quantification of gypsum crystal nucleation, growth, and breakage rates in a wet flue gas desulfurization pilot plant

    SciTech Connect

    Hansen, B.B.; Kiil, S.; Johnsson, J.E.

    2009-10-15

    The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(V) SO{sub 2} gas stream, displayed a strong nonlinear behaviour (in a ln(n(l)) vs. I plot) at the lower end of the particle size range, compared to the well-known linear mixed suspension mixed product removal model. A transient population balance breakage model, fitted to experimental data, was able to model an increase in the fraction of small particles, but not to the extent observed experimentally. A three-parameter, size-dependent growth model, previously used for sodium sulphate decahydrate and potash alum, was able to describe the experimental data, indicating either size-dependent integration kinetics or growth rate dispersion.

  5. Two-step nucleation of the g-phase in a Ti-45Al-18Nb alloy

    SciTech Connect

    Goyel, Sonalika; Rios, Orlando; Kesler, Michael; Ebrahimi, Fereshteh

    2010-01-01

    Phase transformations in a high Nb TieAleNb alloy (Ti-45Al-18Nb at%) upon cooling were studied. This alloy solidifies as single b-phase, which upon cooling under equilibrium conditions, is expected to follow the b / b g / b g s / g s transformation path. The DTA analysis confirmed two transformation events as manifested by two peaks upon cooling. However, compositional and structural characterization of samples with different heat treatment schedules, including slow cooling (9 C/min), revealed that the s-phase did not form upon cooling. The two DTA peaks observed in the cooling cycle of the alloy are proven to be associated with the two-stage formation of the g-phase. Detailed microstructural evaluations showed that the g-phase nucleated in two discrete stages and exhibited two different morphologies. The absence of the s-phase is believed to be due to the lack of enough driving force at high temperatures. The aging of a fast cooled sample, yielding an equilibrated microstructure, substantiated the presence of the s-phase.

  6. Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

    2002-01-01

    Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

  7. GAS PHASE EXPOSURE HISTORY DERIVED FROM MATERIAL PHASE CONCENTRATION PROFILES USING SOLID PHASE MICRO-EXTRACTION

    EPA Science Inventory

    EPA Identifier: F8P31059
    Title: Gas Phase Exposure History Derived from Material Phase Concentration Profiles Using Solid Phase Micro-Extraction
    Fellow (Principal Investigator): Jonathan Lewis McKinney
    Institution: University of Missouri - ...

  8. The physical chemistry of nucleation of sub-micrometer non-oxide ceramic powders via sub-oxide vapor-phase reduction reaction

    SciTech Connect

    Jha, A.

    1996-10-01

    Fine ceramic powders (< 500 nm) exhibit exceptional physical and mechanical properties in engineered structural ceramics. The production of fine powders, in particular the non-oxide ceramics, via a cheaper route than the organic solvent route has been rather elusive. This paper examines the physical chemistry of sub-oxide vapor-phase reduction reaction for the nucleation of non-oxide ceramic phase. Well known vapor species eg SiO and BO in the production of technical ceramic powders (SiC, BN) are particularly discussed for understanding the nucleation process of SiC and BN ceramic phases respectively. The regimes of partial pressures and temperatures are particularly identified. The calculated nucleation rate as a function of the temperature is compared with the experimental results on powder morphology. The production of amorphous and nanocrystalline h-BN powders is discussed in the context of substrate structure and thermodynamic parameters.

  9. Project ARGO: Gas phase formation in simulated microgravity

    NASA Technical Reports Server (NTRS)

    Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

    1993-01-01

    The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

  10. Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation

    NASA Technical Reports Server (NTRS)

    Matsumoto, Y.

    1988-01-01

    The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.

  11. Atmospheric nucleation: Measurements, mechanisms, and dynamics

    NASA Astrophysics Data System (ADS)

    Kuang, Chongai

    New particle formation by nucleation of gas-phase species significantly influences the size distributions and number concentrations of atmospheric aerosols. These nucleated particles are formed at rates that are orders of magnitude higher than were predicted by early models and grow at rates that are typically ten times faster than can be explained by the condensation of sulfuric acid alone. The resultant aerosols exert a significant impact on global climate by affecting the earth's radiation balance directly through the scattering and absorption of incident solar radiation, and indirectly through their role as cloud condensation nuclei (CCN). High formation rates and fast growth to CCN sizes ensure that NPF contributes significantly to the global CCN population. It is the primary goal of the research described in this thesis to develop robust models, constrained by measurement, for the sequential formation of CCN from the nucleation of gas-phase precursors. To this end, my thesis focuses on four topics: the development of nucleation rate parameterizations from correlations between formation rates of 1 nm particles and gas-phase sulfuric acid concentrations in diverse environments; the development of a cluster formation mechanism incorporating energetic barriers at the smallest clusters; the derivation of a simple, dimensionless criterion determining whether or not NPF would occur on a particular day; and the determination of the survival probability of newly formed particles (3 nm) as they grow to a CCN-active size (100 nm).

  12. Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars

    NASA Technical Reports Server (NTRS)

    Whitmire, D. P.; Matese, John J.; Reynolds, R. T.

    1989-01-01

    A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.

  13. Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films

    NASA Technical Reports Server (NTRS)

    Roberts, F. E.

    2003-01-01

    A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.

  14. Real Gas/Blunt Cone. Phase 2

    NASA Technical Reports Server (NTRS)

    Deiwert, George S.; Eitelberg, Georg

    1998-01-01

    In this chapter recent activity in real-gas database definition and code validation will be summarized. In the Phase I report of the Working Group (WG) 181, aerothermodynamic problems were classified, for purpose of discussion, into seven types: aerodynamic parameters, viscous/shock interaction, boundary-layer transition, forebody-heating/heat-transfer, radiation and ablation, lee and base-region flow, and low-density flow. Several of these problem types were the subject of various chapters of the Phase 1 report describing real-gas effects and ground test facility issues. In this chapter some background and objectives outlined in the real-Gas effects Chapter V of the Phase 1 report will be reviewed. The results of the blunt cone test campaign developed under the auspices of the WG18 activity to study real-gas phenomena will be summarized, including the experimental and computational programs, issues and questions, and recommendations. Further, recent progress in other real-gas areas beyond the blunt cone test campaign will be discussed. Finally, a summary in which the present status of our understanding of real-gas issues will be presented.

  15. Sizes of nanobubbles from nucleation rate measurements

    NASA Astrophysics Data System (ADS)

    Wilemski, G.

    2003-03-01

    In homogeneous bubble nucleation, the critical nucleus typically has nanometer dimensions. The volume V of a critical bubble can be determined from the simple equation (partial W/partial p)_T=V, where W is the reversible work of nucleus formation and p is the ambient pressure of the liquid phase in which bubble formation is occurring. The relation, W/kT=-ln J+ln A, where J is the steady state nucleation rate and A is the weakly pressure-dependent kinetic prefactor, allows V to be determined from rate measurements. The original derivation of this equation for V from the nucleation theorem was limited to one-component, ideal gas bubbles with a gas density much smaller than that of the ambient liquid. [D. Kashchiev, Nucleation: basic theory with applications (Butterworth-Heinemann, Oxford, 2000) p. 226.] The result is actually much more general, and it will be shown that it applies to multi-component, nonideal gas bubbles, provided the same density inequality holds. When the bubble phase and liquid densities are comparable, a more complicated, but also general and rigorous result is found.

  16. Gas-Phase Infrared; JCAMP Format

    National Institute of Standards and Technology Data Gateway

    SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

  17. Continuous-Flow Gas-Phase Bioreactors

    NASA Technical Reports Server (NTRS)

    Wise, Donald L.; Trantolo, Debra J.

    1994-01-01

    Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

  18. EPA GAS PHASE CHEMISTRY CHAMBER STUDIES

    EPA Science Inventory

    Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

  19. Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases. [in planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Dunder, T.; Clapp, M. L.; Miller, R. E.

    1993-01-01

    It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.

  20. Nucleation and temperature-driven phase transitions of silicene superstructures on Ag(1?1?1)

    NASA Astrophysics Data System (ADS)

    Grazianetti, C.; Chiappe, D.; Cinquanta, E.; Fanciulli, M.; Molle, A.

    2015-06-01

    Silicene grown on Ag(1?1?1) is characterized by several critical parameters. Among them, the substrate temperature plays a key role in determining the morphology during growth. However, an unexpected important role is also equally played by the post-deposition annealing temperature which determines the self-organization of silicene domains even in the submonolayer coverage regime and consecutive transitions between silicene with different periodicity. These temperature-driven phase transitions can be exploited to select the desired majority silicene phase, thus allowing for the manipulation of silicene properties.

  1. Nucleation and temperature-driven phase transitions of silicene superstructures on Ag(1?1?1).

    PubMed

    Grazianetti, C; Chiappe, D; Cinquanta, E; Fanciulli, M; Molle, A

    2015-07-01

    Silicene grown on Ag(1?1?1) is characterized by several critical parameters. Among them, the substrate temperature plays a key role in determining the morphology during growth. However, an unexpected important role is also equally played by the post-deposition annealing temperature which determines the self-organization of silicene domains even in the submonolayer coverage regime and consecutive transitions between silicene with different periodicity. These temperature-driven phase transitions can be exploited to select the desired majority silicene phase, thus allowing for the manipulation of silicene properties. PMID:26020358

  2. Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases

    NASA Astrophysics Data System (ADS)

    Dunder, T.; Clapp, M. L.; Miller, R. E.

    1993-01-01

    It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.

  3. Activated carbon for gas phase arsenic capture

    SciTech Connect

    Jadhav, R.; Gupta, H.; Misro, S.; Agnihotri, R.; Fan, L.S.

    1999-07-01

    Investigation of activated carbon as a multifunctional sorbent for trace metal capture is the focus of this study. In addition to mercury and halides, selenium and arsenic represent two of the most volatile trace species that remain in gas phase in substantial amounts. In this work, fundamental sorption characteristics of the activated carbon for arsenic removal from the gas phase are investigated. Activated carbons with different structural properties are studied for their usefulness in removing arsenic species from flue gas. Arsenic oxide (As{sub 2}O{sub 3}) is used as the source of arsenic. Preliminary sorption studies indicate that arsenic removal occurs by physical adsorption, with increased capture by carbons with higher surface areas.

  4. Initial nucleation site formation due to acoustic droplet vaporization

    NASA Astrophysics Data System (ADS)

    Li, David S.; Kripfgans, Oliver D.; Fabiilli, Mario L.; Brian Fowlkes, J.; Bull, Joseph L.

    2014-02-01

    Acoustic droplet vaporization (ADV) is the selective vaporization of liquid microdroplets using ultrasound, resulting in gas bubbles. The ADV process has been proposed as a tool in biomedical applications such as gas embolotherapy, drug delivery, and phase-change contrast agents. Using a 7.5 MHz focused transducer, the initial gas nucleus formed in perfluorocarbon microdroplets was directly visualized using ultra-high speed imaging. The experimental results of initial nucleation site location were compared to a 2D axisymmetric linear acoustic model investigating the focal spot of the acoustic wave within the microdroplets. Results suggest a wavelength to droplet diameter dependence on nucleation site formation.

  5. Isothermal nucleation and growth kinetics of Pd/Ag alloy phase via in-situ time-resolved high-temperature x-ray diffraction (HTXRD) analysis

    SciTech Connect

    Ayturk, Mahmut Engin; Payzant, E Andrew; Speakman, Scott A; Ma, Yi Hua

    2008-01-01

    Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex-situ studies carried by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in-situ time-resolved high temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 C, 550 C and 600 C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500oC, 550oC and 600oC, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. The cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 and 185.6 kJ/mol and in excellent agreement with the literature values (183-239.5 kJ/mol).

  6. Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process

    NASA Astrophysics Data System (ADS)

    Kumar, S. Girish; Rao, K. S. R. Koteswara

    2014-09-01

    Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

  7. Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process.

    PubMed

    Kumar, S Girish; Rao, K S R Koteswara

    2014-10-21

    Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested. PMID:24969423

  8. Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

    NASA Astrophysics Data System (ADS)

    Qazi, H. I. A.; Nie, Qiu-Yue; Li, He-Ping; Zhang, Xiao-Fei; Bao, Cheng-Yu

    2015-12-01

    This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up the generation of OH (A-X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.

  9. The homogeneous nucleation of 1-pentanol in a laminar flow diffusion chamber: the effect of pressure and kind of carrier gas.

    PubMed

    Brus, D; Hyvrinen, A-P; Wedekind, J; Viisanen, Y; Kulmala, M; Zdmal, V; Smolk, J; Lihavainen, H

    2008-04-01

    The influence of total pressure and kind of carrier gas on homogeneous nucleation rates of 1-pentanol was investigated using experimental method of laminar flow diffusion chamber in this study. Two different carrier gases (helium and argon) were used in the total pressure range from 50 to 400 kPa. Nucleation temperatures ranged from 265 to 290 K for 1-pentanol-helium and from 265 to 285 K for 1-pentanol-argon. Nucleation rates varied between 10(1) and 10(6) cm(-3) s(-1) for 1-pentanol-helium and between 10(2) and 10(5) cm(-3) s(-1) for 1-pentanol-argon. Both positive and slight negative pressure effects were observed depending on temperature and carrier gas. The trend of pressure effect was found similar for both carrier gases. Error analysis on thermodynamic properties was conducted, and the lowering of surface tension due to adsorption of argon on nucleated droplets was estimated. A quantitative overview of pressure effect is provided. PMID:18397069

  10. Centrifugal Liquid/Gas Separator With Phase Detectors

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.

    1994-01-01

    Centrifugal liquid/gas separator that includes phase (liquid or gas) detectors helps ensure exclusiveness of each phase at its assigned outlet. Acoustic sensors in centrifugal liquid/gas separator measure speeds of sound in nominally pure liquid and nominally pure gas at liquid and gas outlets respectively. When speed of sound is that of pure liquid or gas, valve opens to let liquid or gas flow out.

  11. Circulating nucleated peripheral blood cells contribute to early-phase meniscal healing.

    PubMed

    Yamasaki, Shinya; Hashimoto, Yusuke; Takigami, Junsei; Terai, Shozaburo; Takahashi, Masafumi; Wakitani, Shigeyuki; Nakamura, Hiroaki

    2014-10-10

    The purpose of this study was to assess how peripheral blood cells (PBCs) contribute to meniscus repair, using a parabiotic rat model. Wild-type (WT) and green fluorescent protein (GFP) transgenic rats were conjoined at the torso. After 4 weeks, the anterior part of the medial meniscus of both groups of rats was removed. At 1, 2, 4, 8 and 12 weeks post-meniscectomy, repaired tissue was evaluated using stereomicroscopy, histology with toluidine blue staining, and immunofluorescence microscopy. Stereomicroscopic observations and confocal laser microscopy revealed that a high number of GFP-positive cells were present in the repaired meniscus of WT rats 1 week post-meniscectomy, and the number of GFP-positive cells decreased over time. Based on blood chimerism, the ratios of PBCs in the repaired meniscus were 20.5??2.3% at 1 week, 8.3??0.9% at 2 weeks, 4.4??0.9% at 4 weeks, 2.1??0.9% at 8 weeks, and 0.5??0.4% at 12 weeks, post-meniscectomy. Histologically, fibrochondrocytes were observed in the repaired meniscus of WT rats after 4 weeks, some of which were GFP-positive. The chondrogenic marker, type II collagen, was merged within the PBCs in the repaired tissue. However, type-II-collagen-positive cell ratio and metachromasia in the repaired meniscus were not equivalent in normal meniscal tissue. This indicated that PBCs were present within the repaired meniscus at an early phase, replacing the excised meniscal cells, suggesting PBCs contributed to meniscal healing. The tissue repair contribution by these cells decreased at later phases. Copyright 2014 John Wiley & Sons, Ltd. PMID:25308161

  12. Receptors useful for gas phase chemical sensing

    DOEpatents

    Jaworski, Justyn W; Lee, Seung-Wuk; Majumdar, Arunava; Raorane, Digvijay A

    2015-02-17

    The invention provides for a receptor, capable of binding to a target molecule, linked to a hygroscopic polymer or hydrogel; and the use of this receptor in a device for detecting the target molecule in a gaseous and/or liquid phase. The invention also provides for a method for detecting the presence of a target molecule in the gas phase using the device. In particular, the receptor can be a peptide capable of binding a 2,4,6-trinitrotoluene (TNT) or 2,4,-dinitrotoluene (DNT).

  13. Gas-phase separations of protease digests.

    PubMed

    Valentine, S J; Counterman, A E; Hoaglund, C S; Reilly, J P; Clemmer, D E

    1998-11-01

    A mixture of peptides from a complete tryptic digest of ubiquitin has been analyzed by ion mobility/time-of-flight mass spectrometry techniques. All components of the mixture were electrosprayed and ions were separated in the gas phase based on differences in their mobilities through helium before being dispersed into a time-of-flight mass spectrometer for mass-to-charge analysis. The data show that ions separate into families primarily according to differences in their charge states and, to a lesser extent, differences in conformation. This approach reduces spectral congestion typically associated with electrosprayed mixtures and provides charge assignments for mass-to-charge ratio data. Gas-phase separations of ions appear to provide a new physical basis for characterizing components of biological mixtures. PMID:9794086

  14. Gas phase chemistry of chlorine nitrate

    SciTech Connect

    Okumura, M.; Moore, T.A.; Crellin, K.C.

    1995-12-31

    Chlorine nitrate (ClONO{sub 2}) is a reservoir of both ClO{sub x} and NO{sub x} radicals in Earth`s stratosphere, and its decomposition is important in determining the abundance of stratospheric ozone. We present experimental and theoretical studies that explore the mechanisms and dynamics of processes leading to ClONO{sub 2} destruction in the stratosphere. Molecular beam photodissociation experiments have been performed to determine the decomposition pathways of ClONO{sub 2} upon excitation at 308 nm and to explore the possibility of a long-lived excited state. We have also investigated the reaction of chlorine nitrate with chloride ions Cl{sup -} in the gas phase. The gas phase ionic reaction may elucidate ionic mechanisms of heterogeneous reactions occurring on the surfaces of Polar Stratospheric Cloud particles and also raise doubts about proposed schemes to mitigate ozone depletion by electrifying the stratosphere.

  15. Fuel Performance Experiments and Modeling: Fission Gas Bubble Nucleation and Growth in Alloy Nuclear Fuels

    SciTech Connect

    McDeavitt, Sean; Shao, Lin; Tsvetkov, Pavel; Wirth, Brian; Kennedy, Rory

    2014-04-07

    Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. Many mechanistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, research, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.

  16. Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.

    PubMed

    Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A

    2011-11-28

    Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, ?, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, ? can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds. PMID:21912788

  17. Surface Bubble Nucleation Stability

    NASA Astrophysics Data System (ADS)

    Seddon, James R. T.; Kooij, E. Stefan; Poelsema, Bene; Zandvliet, Harold J. W.; Lohse, Detlef

    2011-02-01

    Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobized silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this parameter space, occurring for gas concentrations of approximately 100%-110%. Below the nanobubble region we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.

  18. Gas phase equilibrium structure of histamine.

    PubMed

    Tikhonov, Denis S; Rykov, Anatolii N; Grikina, Olga E; Khaikin, Leonid S

    2016-02-17

    The first gas electron diffraction (GED) experiment for histamine was carried out. The equilibrium structure of histamine in the gas phase was determined on the basis of the data obtained. The refinement was also supported by the rotational constants obtained in previous studies [B. Vogelsanger, et al., J. Am. Chem. Soc., 1991, 113, 7864-7869; P. Godfrey, et al., J. Am. Chem. Soc., 1998, 120, 10724-10732] and quantum chemical calculations. The proposed mechanism of tautomerization by simultaneous intermolecular transfer of hydrogens in a histamine dimer helps to explain the distribution of tautomers in different experiments. The estimations of the conformational interconversion times provided the explanation for the absence of some conformers in the rotational spectroscopy experiments. PMID:26845147

  19. Gas-phase photolysis of tungsten hexachloride

    NASA Astrophysics Data System (ADS)

    Kullmer, R.

    1994-07-01

    The laser-induced decomposition of WCl6 in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar+-laser radiation dissociation of WCl6 into WCl4 and Cl2 has been observed. Further decomposition can be achieved in the presence of H2 employing ultraviolet Ar+-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.

  20. Gas phase thermochemistry of organogermanium compounds

    SciTech Connect

    Engel, J.P.

    1993-12-07

    A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

  1. Cavitation nucleation

    NASA Astrophysics Data System (ADS)

    Crum, Lawrence A.

    2001-05-01

    For his dissertation research at Harvard, Bob Apfel chose the subject of homogeneous nucleation, and conceived of some ingenious experiments to test existing theories. By selecting a small microdroplet of liquid, he could make the reasonable assumption that no inhomogeneities were present to serve as preferential sites for liquid rupture. However, Bob also studied dirty liquids, as well as very clean ones, and wrote some seminal papers on inhomogeneous nucleation, in which he developed the Golden rule: Know thy liquid! Currently, considerable attention has been devoted to the study of cavitation generation in vivo, particularly in blood, and, for this case, the nucleation conditions are much different than those for normal liquids. In this presentation, I will review some of Bob's pioneering studies and present some of our latest studies of cavitation inception, both in vitro and in vivo.

  2. Vaccum Gas Tungsten Arc Welding, phase 1

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

    1995-01-01

    This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

  3. Vaccum Gas Tungsten Arc Welding, phase 1

    NASA Astrophysics Data System (ADS)

    Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

    1995-03-01

    This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

  4. Giddings Austin chalk enters deep lean-gas phase

    SciTech Connect

    Moritis, G.

    1995-12-25

    Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.

  5. Multinuclear NMR spectroscopy in the gas phase

    NASA Astrophysics Data System (ADS)

    Jackowski, K.

    2006-04-01

    Nuclear magnetic resonance (NMR) of some nuclei (e.g. 1H, 13C, 19F, 29Si or 31P, I=1/2) gives strong signals which allow analytical studies of gaseous compounds. The other magnetic nuclei have low natural abundance or/and contain an electric quadrupole moment and their NMR signals are rather weak. In our laboratory we have developed new experimental techniques, which permit us to monitor several micrograms of chemical compounds in gaseous matrices. Applying this approach we have observed magnetic shielding of various nuclei, including 17O and 33S at the natural abundance, in the gas phase as a function of density. Density-dependent spin-spin couplings were also found for many chemical compounds. It has been shown that NMR gas-phase studies can easily be extended on molecules, which exhibit strong intermolecular interactions and are liquids at room temperature. All the latter NMR experimental results obtained for gaseous matrices are reviewed in this paper.

  6. The impact of microphysical parameters, ice nucleation mode, and habit growth on the ice/liquid partitioning in mixed-phase Arctic clouds

    NASA Astrophysics Data System (ADS)

    Ervens, Barbara; Feingold, Graham; Sulia, Kara; Harrington, Jerry

    2011-09-01

    The fundamental physical processes that maintain supercooled liquid in observed Arctic mixed-phase clouds are poorly constrained. To isolate the factors that control ice/liquid partitioning during the ascent of an air parcel, we apply an adiabatic parcel model that includes ice nucleation by deposition and immersion freezing and ice habit evolution. Simulations are performed for two different temperature regimes that resemble those observed during the Mixed-Phase Arctic Cloud Experiment (-13C < T < -9C) and the Surface Heat Budget of the Arctic Ocean (-22C < T < -17C). Effects on ice and liquid water evolution in an updraft are explored as a function of ice nucleus (IN) concentration and nucleation mode, updraft velocity, properties of cloud condensation nuclei, and assumption about ice particle shape (habit). For most conditions, ice and liquid coexist and increase simultaneously, and only at high IN concentrations or low updraft velocities do ice particles grow at the expense of droplets. The impact of the ice nucleation mode on ice/liquid distribution depends on the temperature and supersaturation regime. The assumption of spherical ice particles instead of nonspherical habits leads to an underestimate of ice growth. It is concluded that updraft velocity, IN concentrations, and particle shape can impact ice/liquid distribution to similar extents.

  7. Monte Carlo simulations of phase transformations caused by nucleation and subsequent anisotropic growth: Extension of the Johnson-Mehl-Avrami-Kolmogorov theory

    NASA Astrophysics Data System (ADS)

    Kooi, B. J.

    2004-12-01

    Monte Carlo (MC) simulations of isothermal phase transformations were performed based on a temperature- and time-dependent nucleation rate and a temperature-dependent and time-independent anisotropic growth rate (linear growth). One- or two-dimensional anisotropic growth in two-dimensional space is considered and nucleation occurs randomly throughout space. The MC simulations show that parallel growth of anisotropically growing transformation products with identical convex shape can be described accurately by the kinetic theory due to Johnson, Mehl, Avrami, and Kolmogorov (JMAK), but nonparallel anisotropic growth, orthogonal in the present work, incorporating blocking up to all relevant orders leads to hard impingement that results in strong deviations from JMAK kinetics. A transparent analytical description extending on, but incorporating the JMAK theory has been developed that turns out to accurately reproduce the numerical results of all present MC simulation, leading to improved understanding of how impingement should be incorporated in JMAK theory.

  8. Molecular Ice Nucleation Activity of Birch Pollen

    NASA Astrophysics Data System (ADS)

    Felgitsch, Laura; Bichler, Magdalena; Häusler, Thomas; Weiss, Victor U.; Marchetti-Deschmann, Martina; Allmaier, Günter; Grothe, Hinrich

    2015-04-01

    Heterogeneous ice nucleation plays a major part in ecosystem and climate. Due to the triggering of ice cloud formation it influences the radiation balance of the earth, but also on the ground it can be found to be important in many processes of nature. So far the process of heterogeneous ice nucleation is not fully understood and many questions remain to be answered. Biological ice nucleation is hereby from great interest, because it shows the highest freezing temperatures. Several bacteria and fungi act as ice nuclei. A famous example is Pseudomonas syringae, a bacterium in commercial use (Snomax®), which increases the freezing from homogeneous freezing temperatures of approx. -40° C (for small volumes as in cloud droplets) to temperatures up to -2° C. In 2001 it was found that birch pollen can trigger ice nucleation (Diehl et al. 2001; Diehl et al. 2002). For a long time it was believed that this is due to macroscopic features of the pollen surface. Recent findings of Bernhard Pummer (2012) show a different picture. The ice nuclei are not attached on the pollen surface directly, but on surface material which can be easily washed off. This shows that not only the surface morphology, but also specific molecules or molecular structures are responsible for the ice nucleation activity of birch pollen. With various analytic methods we work on elucidating the structure of these molecules as well as the mechanism with which they trigger ice nucleation. To solve this we use various instrumental analytic techniques like Nuclear Magnetic Resonance spectroscopy (NMR), Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), and Gas-phase Electrophoretic Mobility Molecular Analysis (GEMMA). Also standard techniques like various chromatographic separation techniques and solvent extraction are in use. We state here that this feature might be due to the aggregation of small molecules, with agglomerates showing a specific surface structure. Our results indicate that the substance is amphiphilic in character leading finally to micelle formation. Diehl, K., Quick, C., Matthias-Maser, S., Mitra, S. K., and Jaenicke, R.: The ice nucleation ability of pollen, part I, Atmos. Res., 58, 75-87, 2001. Diehl, K., Matthias-Maser, S., Jaenicke, R., and Mitra, S. K.: The ice nucleation ability of pollen, part II, Atmos. Res., 61, 125-133, 2002. Pummer, B., Bauer, H., Bernardi, J., Bleicher, S., Grothe, H.; Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen; Atmos. Chem. Phys., 12, 2541 - 2550, 2012.

  9. Kinetic studies of gas phase free radicals

    NASA Astrophysics Data System (ADS)

    Wittig, C.; Reisler, H.

    1982-11-01

    Detailed studies of elementary unimolecular and bimolecular gas phase processes were carried out using the time resolved techniques of laser photolysis and laser induced fluorescence. Bimolecular reactions of diatomic and triatomic carbon and the ethynyl radical with small polyatomic molecules were investigated, and rate coefficients and energy disposal into product degrees of freedom were determined. The study of unimolecular reactions induced by multiple photon excitation concentrated on simple bond fission reactions. Nascent rovibronic state distributions in the dissociation products of trifluoroacetonitrile were determined as a function of laser fluence and intensity. The rate of the unimolecular reaction of 2-methyl-2-nitrosopropane was measured following dye laser excitation, and found to be faster than the rate deduced from thermal activation experiments.

  10. Dependence of nucleation rates on sulfuric acid vapor concentration in PoValley, Italy

    NASA Astrophysics Data System (ADS)

    Hamed, Amar; Pla-Dlmer, Christian; Elste, Thomas; Stange, Georg; Decesari, Stefano; Carbone, Claudio; Facchini, Maria Cristina; Joutsensaari, Jorma; Laaksonen, Ari

    2010-05-01

    A field campaign was conducted at the polluted rural site, San Pietro Capofiume (SPC) in PoValley, Italy, from June 26th to July 12th 2009 in the framework of the EUCAARI (European integrated project on aerosol, cloud, climate, and air interactions) project. The gas-phase sulfuric acid concentrations were measured for the first time at SPC station during this campaign. Here we examine the dependence of nucleation rate on sulfuric acid vapor concentrations in SPC. The apparent nucleation rate - i.e. formation rate of 3 nm particles - was directly determined from differential mobility particle sizer data. The nucleation rate at 1 nm (J1) was then calculated by accounting for the coagulation of the sub-3 nm clusters with large particles during their growth from 1 to 3 nm. The dependence of J1 on [H2SO4] was studied for each nucleation day individually and for all nucleation days as a whole. It is usually assumed that the dependence of nucleation rate on sulfuric acid concentration follows a simple power law model J1 = P [H2SO4]^n; where P is the prefactor containing chemical and physical information of the nucleation process, and n is the nucleation exponent. With the so called activation and kinetic nucleation mechanisms, n takes the values 1 and 2, respectively, and most field studies show n to fall between these two values. For the SPC data, the nucleation exponent was higher than 2 for both individual days and for all nucleation days as a whole. In the light of the obtained results we will discuss the nucleation mechanism, composition of the nucleation mode particles, and the role of other gases (such as ammonia and water vapor) in the formation of new particles in SPC in more detail.

  11. Gas: A Neglected Phase in Remediation of Metals and Radionuclides

    SciTech Connect

    Denham, Miles E.; Looney, Brian B

    2005-09-28

    The gas phase is generally ignored in remediation of metals and radionuclides because it is assumed that there is no efficient way to exploit it. In the literal sense, all remediations involve the gas phase because this phase is linked to the liquid and solid phases by vapor pressure and thermodynamic relationships. Remediation methods that specifically use the gas phase as a central feature have primarily targeted volatile organic contaminants, not metals and radionuclides. Unlike many organic contaminants, the vapor pressure and Henry's Law constants of metals and radionuclides are not generally conducive to direct air stripping of dissolved contaminants. Nevertheless, the gas phase can play an important role in remediation of inorganic contaminants and provide opportunities for efficient, cost effective remediation. The objective here is to explore ways in which manipulation of the gas phase can be used to facilitate remediation of metals and radionuclides.

  12. Four-phase fully-coupled mold-filling and solidification simulation for gas porosity prediction in aluminum sand casting

    NASA Astrophysics Data System (ADS)

    Jakumeit, J.; Jana, S.; Waclawczyk, T.; Mehdizadeh, A.; Sadiki, A.; Jouani, J.

    2012-07-01

    The impact of mold-filling and oxide film enclosure on gas porosity in A356 was investigated using a three-phase, fully-coupled, mold-filling and solidification simulation. For the prediction of gas porosity, a fourth hydrogen phase was added. At the solidification front hydrogen is rejected from the solid and accumulates in the melt. Pores nucleate if the solute gas exceeds the solubility limit. Air and melt are separated by a volume of fluid interface and special treatment of the hydrogen phase convection was necessary to limit the hydrogen to the melt. Folding of the melt surface was used as a source for oxide film entrainment. These oxide films were transported with the melt and used as nucleation sites for gas porosity formation. The influence of melt flow due to filling and oxide film distribution was analyzed using a simple 3-block test geometry. The test geometry was cast in A356 and analyzed by computer tomography to validate the porosity prediction.

  13. Nucleation at the contact line observed on nanotextured surfaces.

    PubMed

    Gurganus, C W; Charnawskas, J C; Kostinski, A B; Shaw, R A

    2014-12-01

    It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with ???/?, where ? is a relevant line tension and ? is the surface tension, range from nanometers to micrometers. It is found that nanoscale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while microscale texture does not. PMID:25526136

  14. Buckyball Nucleation of HiPco Tubes

    NASA Technical Reports Server (NTRS)

    Smalley, Richard E.

    2012-01-01

    The purpose of this innovation is to enhance nucleation of single-wall nanotubes (SWNTs) in the HiPco process, selectively producing 10,10 tubes, something which until now has not been thought possible. This is accomplished by injecting C60, or a derivative of C60, solubilized in supercritical CO2 together with a transition metal carboneal cocatalyst into the HiPco reactor. This is a variant on the supercritical disclosure. C60 has never been used to nucleate carbon nanotubes in the gas phase. C60 itself may not have adequate solubility in supercritical CO2. However, fluorinated C60, e.g., C60F36, is easy to make cheaply and should have much enhanced solubility.

  15. Solid-liquid surface tensions of critical nuclei and nucleation barriers from a phase-field-crystal study of a model binary alloy using finite system sizes

    NASA Astrophysics Data System (ADS)

    Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin

    2014-08-01

    Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007), 10.1103/PhysRevB.75.064107] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula.

  16. Aerosol Nucleation Rates of Sulfuric Acid and Water Measured Under the Lower Tropospheric Conditions

    NASA Astrophysics Data System (ADS)

    Young, L.; Benson, D. R.; Quinn, K.; Lee, S.

    2006-12-01

    Nucleation is a gas to particle conversion process in which solid or liquid aerosol particles form directly from the gas phase species and thus is an important step in the chain of reactions that lead to cloud formation. However, the nucleation mechanisms are poorly understood. There are presently large discrepancies amongst the measured nucleation rates by different laboratory studies; nucleation rates taken under the atmospheric conditions are very rare. We perform laboratory experiments of aerosol nucleation under the atmospheric conditions with a novel chemical ionization mass spectrometer (CIMS) and nano-particle differential mobility analyzer (Nano-DMA) and water condensation nuclei counter (WCPC). Our CIMS measures low concentrations of sulfuric acid (down to 1e-6 cm-3). Measurements of Nano-DMA and WCPC provide aerosol nucleation rates. An atmospheric pressure flow reactor is used to photochemically produce sulfuric acid particles from the reactions of OH and sulfur dioxide. Sulfur dioxide is also detected by CIMS. OH forms from the photo-dissociation of water vapor using a mercury lamp and the OH concentrations are calculated based on the known photochemical reaction rates and measured photon fluxes. This OH generation method also allows for sulfuric acid calibration. We will present nucleation rates of sulfuric acid and water as a function of sulfuric acid concentration, RH and temperature under the conditions of lower troposphere. We also compare these results with those by Berndt et al. (2005) that show relatively high concentrations of sulfuric acid and water nucleation rates comparable to the atmospheric observations.

  17. Spaceborne lidar observations of the ice-nucleating potential of dust, polluted dust, and smoke aerosols in mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Tan, Ivy; Storelvmo, Trude; Choi, Yong-Sang

    2014-06-01

    Previous laboratory studies and in situ measurements have shown that dust particles possess the ability to nucleate ice crystals, and smoke particles to some extent as well. Even with coatings of pollutants such as sulphate and nitrate on the surface of dust particles, it has been shown that polluted dust particles are still able to nucleate ice in the immersion, deposition, condensation, and contact freezing modes, albeit less efficiently than unpolluted dust. The ability of these aerosols to act as ice nuclei in the Earth's atmosphere has important implications for the Earth's radiative budget and hence global climate change. Here we determine the relationship between cloud thermodynamic phase and dust, polluted dust, and smoke aerosols individually by analyzing their vertical profiles over a ˜5 year period obtained by NASA's spaceborne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization. We found that when comparing the effects of temperature and aerosols, temperature appears to have the dominant influence on supercooled liquid cloud fraction. Nonetheless, we found that aerosols still appear to exert a strong influence on supercooled liquid cloud fraction as suggested by the existence of negative temporal and spatial correlations between supercooled liquid cloud fraction and frequencies of dust aerosols from around the world, at the -10°C, -15°C, -20°C, and -25°C isotherms. Although smoke aerosol frequencies were also found to be negatively correlated with supercooled liquid cloud fraction, their correlations are weaker in comparison to those between dust frequencies and supercooled liquid cloud fraction. For the first time, we show this based on observations from space, which lends support to previous studies that dust and potentially smoke aerosols can globally alter supercooled liquid cloud fraction. Our results suggest that the ice-nucleating ability of these aerosols may have an indirect climatic impact that goes beyond the regional scale, by influencing cloud thermodynamic phase globally.

  18. Nucleation in the presence of long-range interactions. [performed on ferroelectric barium titanate

    NASA Technical Reports Server (NTRS)

    Chandra, P.

    1989-01-01

    Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

  19. Hydrocarbon radical thermochemistry: Gas-phase ion chemistry techniques

    SciTech Connect

    Ervin, Kent M.

    2014-03-21

    Final Scientific/Technical Report for the project "Hydrocarbon Radical Thermochemistry: Gas-Phase Ion Chemistry Techniques." The objective of this project is to exploit gas-phase ion chemistry techniques for determination of thermochemical values for neutral hydrocarbon radicals of importance in combustion kinetics.

  20. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  1. Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber

    SciTech Connect

    Gallavardin, S. J.; Froyd, Karl D.; Lohmann, U.; Moehler, Ottmar; Murphy, Daniel M.; Cziczo, Dan

    2008-08-26

    Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or interstitial aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particles were more effective ice nuclei (IN) than similar particles with a coating. Metallic particles from contamination in the chamber initiated ice nucleation before other species but there were few enough that they did not compromise the experiments. Nitrate, sulfate, and organics were often detected on particles and ice residue, evidently from scavenging of trace gas-phase species in the chamber. Hematite was a more effective ice nucleus than illite. Ice residue was frequently larger than unactivated test aerosol due to the formation of aggregates due to scavenging, condensation of contaminant gases, and the predominance of larger aerosol in nucleation.

  2. Phase Separation in a Polarized Fermi Gas at Zero Temperature

    SciTech Connect

    Pilati, S.; Giorgini, S.

    2008-01-25

    We investigate the phase diagram of asymmetric two-component Fermi gases at zero temperature as a function of polarization and interaction strength. The equations of state of the uniform superfluid and normal phase are determined using quantum Monte Carlo simulations. We find three different mixed states, where the superfluid and the normal phase coexist in equilibrium, corresponding to phase separation between (a) the polarized superfluid and the fully polarized normal gas, (b) the polarized superfluid and the partially polarized normal gas, and (c) the unpolarized superfluid and the partially polarized normal gas.

  3. Metadynamics studies of crystal nucleation

    PubMed Central

    Giberti, Federico; Salvalaglio, Matteo; Parrinello, Michele

    2015-01-01

    Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation. PMID:25866662

  4. Investigating the Microphysics of Arctic Mixed-Phase Clouds using Large Eddy Simulations: The Importance of Liquid-Dependent Ice Nucleation

    NASA Astrophysics Data System (ADS)

    Young, Gillian; Connolly, Paul J.; Jones, Hazel M.; Choularton, Thomas W.; Gallagher, Martin W.; Crosier, Jonathan; Lloyd, Gary; Bower, Keith N.

    2015-04-01

    Our ability to comprehend and accurately model the Arctic climate is currently hindered by a lack of observations of the atmospheric processes unique to this region. A significant source of uncertainty in such models may be found in our representation of aerosol-cloud interactions [1]: for example, there are unanswered questions concerning the relationship between the ice-nucleating Arctic aerosol and the unique cloud microphysics observed in this region [2]. In an effort to address this issue, the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign of 2013 was conducted in the vicinity of the Svalbard archipelago, carrying out in-situ airborne observations of the mixed-phase clouds in this region. This campaign was split into two segments - one in spring, the other in summer - with airborne- and surface-based measurement platforms utilised in each. During the spring campaign, a range of microphysics and remote-sensing instruments were active on board the Facility for Airborne Atmospheric Measurements' (FAAM) BAe146 aircraft to produce a detailed record of the observed Arctic atmosphere. These data were used to conduct a modelling investigation with a focus on ice nucleation: the Large Eddy Model (LEM) - a cloud-resolving model developed by the UK Met Office - was initialised from these observations and simulations were performed to allow the resultant cloud evolution, structure and microphysics to be examined. Models on various scales notoriously have issues with reproducing persistent, mixed-phase Arctic clouds [2,3] and, upon first inspection, the LEM was no different: the modelled cloud dissipated quickly, thus inaccurately replicating the long-lived, mixed-phase clouds observed. However, by considering the discrepancies between the model output and aircraft observations, the treatment of cloud microphysics within the LEM has been developed to improve the simulation of the observed clouds. A long-lived, mixed-phase cloud of similar microphysical properties to those observed is achieved, providing an indication that the realistic simulation of Arctic clouds is strongly dependent on the ice nucleus parameterisation used. References: [1] Curry, J. A. et al., 1996. Overview of Arctic Cloud and Radiation Characteristics. Journal of Climate, 9, 1731-1764. [2] Prenni, A. J. et al., 2007. Can Ice-Nucleating Aerosols Affect Arctic Seasonal Climate? Bulletin of the American Meteorological Society, 88, 541-550. [3] Morrison, H. et al., 2012. Resilience of persistent Arctic mixed-phase clouds. Nature Geoscience, 5, 11-17.

  5. Gas-phase nitronium ion affinities.

    PubMed Central

    Cacace, F; de Petris, G; Pepi, F; Angelelli, F

    1995-01-01

    Evaluation of nitronium ion-transfer equilibria, L1NO2+ + L2 = L2NO2+ + L1 (where L1 and L2 are ligands 1 and 2, respectively) by Fourier-transform ion cyclotron resonance mass spectrometry and application of the kinetic method, based on the metastable fragmentation of L1(NO2+)L2 nitronium ion-bound dimers led to a scale of relative gas-phase nitronium ion affinities. This scale, calibrated to a recent literature value for the NO2+ affinity of water, led for 18 ligands, including methanol, ammonia, representative ketones, nitriles, and nitroalkanes, to absolute NO2+ affinities, that fit a reasonably linear general correlation when plotted vs. the corresponding proton affinities (PAs). The slope of the plot depends to a certain extent on the specific nature of the ligands and, hence, the correlations between the NO2+ affinities, and the PAs of a given class of compounds display a better linearity than the general correlation and may afford a useful tool for predicting the NO2+ affinity of a molecule based on its PA. The NO2+ binding energies are considerably lower than the corresponding PAs and well below the binding energies of related polyatomic cations, such as NO+, a trend consistent with the available theoretical results on the structure and the stability of simple NO2+ complexes. The present study reports an example of extension of the kinetic method to dimers, such as L1(NO2+)L2, bound by polyatomic ions, which may considerably widen its scope. Finally, measurement of the NO2+ affinity of ammonia allowed evaluation of the otherwise inaccessible PA of the amino group of nitramide and, hence, direct experimental verification of previous theoretical estimates. PMID:11607578

  6. [Effect of inert gas xenon on the functional state of nucleated cells of peripheral blood during freezing].

    PubMed

    Laptev, D S; Polezhaeva, T V; Zaitseva, O O; Khudyakov, A N; Utemov, S V; Knyazev, M G; Kostyaev, A A

    2015-01-01

    A new method of preservation of nucleated cells in the electric refrigerator with xenon. After slow freezing and storage is even one day at -80 C persists for more than 60% leukocytes. Cell membranes are resistant to the vital dye. In 85% of granulocytes stored baseline lysosomal-cationic protein, reduced lipid peroxidation and antioxidant activity. Cryopreservation of biological objects in inert gases is a promising direction in the practice of medicine and can be an alternative to the traditional method using liquid nitrogen. PMID:26027341

  7. Bubble nucleation in stout beers.

    PubMed

    Lee, W T; McKechnie, J S; Devereux, M G

    2011-05-01

    Bubble nucleation in weakly supersaturated solutions of carbon dioxide-such as champagne, sparkling wines, and carbonated beers-is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets. PMID:21728549

  8. Bubble nucleation in stout beers

    NASA Astrophysics Data System (ADS)

    Lee, W. T.; McKechnie, J. S.; Devereux, M. G.

    2011-05-01

    Bubble nucleation in weakly supersaturated solutions of carbon dioxide—such as champagne, sparkling wines, and carbonated beers—is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets.

  9. [On road particle emission characteristics of a Chinese phase IV natural gas bus].

    PubMed

    Lou, Di-Ming; Cheng, Wei; Feng, Qian

    2014-03-01

    An on-road experimental research was made on a Chinese phase IV natural gas bus using a Portable Emission Measurement System (PEMS), and particle emission characteristics under different vehicle speed, acceleration and vehicle specific power were investigated. The results show that particle number and mass emission rates increase and their emission factors decrease while the speed of the bus rises. Particle number concentration of different sizes shows multimodal logarithmic distribution pattern when the bus runs on all operation conditions (idle, low speed, medium speed and high speed), and nucleation mode particle account for a large proportion in the total particle number. With the increase of acceleration, particle emission rate rises, and it is lower when the bus runs at constant speed or slow deceleration condition than that at the fast acceleration condition. Furthermore, particle emission rate increases against the absolute value of the vehicle specific power (VSP). PMID:24881371

  10. A dynamic phase-field model for structural transformations and twinning: Regularized interfaces with transparent prescription of complex kinetics and nucleation. Part II: Two-dimensional characterization and boundary kinetics

    NASA Astrophysics Data System (ADS)

    Agrawal, Vaibhav; Dayal, Kaushik

    2015-12-01

    A companion paper presented the formulation of a phase-field model - i.e., a model with regularized interfaces that do not require explicit numerical tracking - that allows for easy and transparent prescription of complex interface kinetics and nucleation. The key ingredients were a re-parametrization of the energy density to clearly separate nucleation from kinetics; and an evolution law that comes from a conservation statement for interfaces. This enables clear prescription of nucleation through the source term of the conservation law and of kinetics through an interfacial velocity field. This model overcomes an important shortcoming of existing phase-field models, namely that the specification of kinetics and nucleation is both restrictive and extremely opaque. In this paper, we present a number of numerical calculations - in one and two dimensions - that characterize our formulation. These calculations illustrate (i) highly-sensitive rate-dependent nucleation; (ii) independent prescription of the forward and backward nucleation stresses without changing the energy landscape; (iii) stick-slip interface kinetics; (iii) the competition between nucleation and kinetics in determining the final microstructural state; (iv) the effect of anisotropic kinetics; and (v) the effect of non-monotone kinetics. These calculations demonstrate the ability of this formulation to precisely prescribe complex nucleation and kinetics in a simple and transparent manner. We also extend our conservation statement to describe the kinetics of the junction lines between microstructural interfaces and boundaries. This enables us to prescribe an additional kinetic relation for the boundary, and we examine the interplay between the bulk kinetics and the junction kinetics.

  11. Ultrafast gas-phase electron diffraction

    NASA Astrophysics Data System (ADS)

    Williamson, Joseph Charles

    1998-03-01

    The temporal resolution of pump-probe, gas-phase electron diffraction (GED) has been extended to the picosecond time scale, a three order-of-magnitude improvement. With such resolution, GED can now be applied to structural studies of fundamental chemical dynamics, providing complementary information to conventional time-resolved spectroscopy techniques. This thesis gives a thorough theoretical and experimental treatment of ultrafast GED. Simulations of coherent chemical dynamics demonstrated that the evolution of molecular spatial coordinates can be determined with fs GED. Similarly, ps GED can reveal the structure of short-lived intermediates in kinetic processes, and the circular symmetries of GED patterns were predicted to break during ps rotational coherences. 620-nm output from an amplified femtosecond laser (2.5 mJ; 300 fs) was split into pump and probe arms and frequency-doubled. 95% of the laser intensity was focused onto a molecular beam. The remaining 5% was directed onto a back-illuminated 450-A silver cathode, where ultrafast electron pulses were created via the photoelectric effect and accelerated to 18 keV. Space-charge effects forced a compromise between electron number density and temporal resolution: streaking experiments revealed that the pulse duration increased by 1 ps for every 1,000 electrons. The electrons intersected the pump laser directly underneath the molecular beam orifice. Approximately 10% of the electrons scattered elastically from sample molecules within the interaction region, and the resulting diffraction pattern was recorded with a scintillator/fused fiber optic/image intensifier/charge- coupled device imaging system. Single-electron sensitivity across two-dimensions was necessary because of the extremely low electron flux, and the measured detective quantum efficiency of the imaging system was better than 0.5. Ground-state GED patterns of several molecules were recorded using ps electron pulses. Time zero for the pump-probe experiment was identified to within 1 ps using photoionization-induced lensing (PIL) of the unscattered electron beam. The first ultrafast GED investigation studied diiodomethane, and diffraction patterns were recorded at several time steps around time zero. The resulting structural transients showed that 10% of the CH2I2 dissociated into CH2I + I following excitation with the 310-nm pump laser. The estimated temporal resolution was 5 to 10 ps.

  12. Real-Time Characterization of Particle and Gas Phase Diesel Emissions - Understanding the Influence of a Diesel Particulate Filter

    NASA Astrophysics Data System (ADS)

    Cross, E. S.; Sappok, A.; Carrasquillo, A. J.; Onasch, T. B.; Fortner, E.; Jayne, J.; Wong, V.; Worsnop, D. R.; Kroll, J. H.

    2010-12-01

    Diesel engine emissions constitute an important source of particulate black carbon (BC) and gas phase organics in the atmosphere. Particles composed of black carbon absorb incoming solar radiation having a net positive radiative forcing effect on the climate. Black carbon also has major air quality implications as BC particles from combustion sources are often coated with poly-aromatic hydrocarbons (PAHs), and are generally emitted in higher concentrations close to population centers. Regulations of diesel emissions target the mass of particulate matter (PM) and concentration of volatile gas phase organic compounds (VOC) produced. A third, potentially important component of diesel exhaust, is low volatility organic compounds (LVOC). Both the VOCs and LVOCs can lead to the formation of ultrafine particles (via homogeneous nucleation) and secondary organic aerosols (via oxidation). Recent development of mass spectrometric techniques to measure particulate black carbon and gas phase organics provide the opportunity to quantify and chemically characterize diesel emissions in real-time. Measurements of both the particulate and gas phase emissions from a medium-duty diesel engine will be presented. The experimental apparatus includes a diesel particulate filter (DPF) integrated in the exhaust line, which is a requirement for all 2007 and newer on-road diesel engines in the U.S. Measurements taken over the regeneration cycle of the DPF provide insight into how this after-treatment technology influences the gas phase and particle phase composition of the emissions. Gas phase measurements were made with a newly developed Total Gas-Phase Organic (TGO) instrument. Particulate species were characterized with a Soot Particle Aerosol Mass Spectrometer (SP-AMS). The combined utility of the TGO and SP-AMS instruments for emissions characterization studies will be demonstrated.

  13. Gas-Liquid Flows and Phase Separation

    NASA Technical Reports Server (NTRS)

    McQuillen, John

    2004-01-01

    Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

  14. Effects of the source temperature on the formation of a metastable HgI 2 phase and consequences for the nucleation and growth behaviors in PVT ampoules

    NASA Astrophysics Data System (ADS)

    Lin, Jun-Xian; Shih, Chen-Tsung; Zhou, Han-Tang; Luo, Ying-Zi; Liao, Jian-Liang; Chiu, Kuan-Cheng

    2006-04-01

    By examining the nucleation and growth phenomena for HgI 2 crystals in physical vapor transport ampoules with a variation of temperatures of the source powder side Tsou and of the crystal growth side Tcry both are near its solid-solid phase transition temperature T=127 C, our experimental results reveal that under Tphase structure of the as-grown HgI 2 crystal is surprisingly governed by Tsou; (2) the temperature range of existence for the metastable ?-HgI 2 phase in crystal growth side is about 17 C below Tc; and (3) by turning a rotating motor to act as mechanical perturbations, this temperature range of existence for ?-phase now reduces to about 11 C below Tc. To explain these phenomena, especially for the metastable ?-phase formed at T

  15. Correlation between nucleation layer structure, dislocation density, and electrical resistivity for GaN films grown on a-plane sapphire by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Twigg, M. E.; Koleske, D. D.; Wickenden, A. E.; Henry, R. L.; Binari, S. C.

    2001-12-01

    Transmission electron microscopy has been used to study AlN nucleation layers (NLs) grown using metalorganic vapor phase epitaxy, in order to link the resistivity of unintentionally doped GaN films to NL microstructure. We observed that high-resistivity (HR) GaN films grew on large-grained NLs, which, in turn, grew on smooth sapphire surfaces. These HR films had a higher density of edge dislocations than screw and mixed dislocations. Low-resistivity GaN films were found to grow on fine-grained NLs that grew on rougher sapphire surfaces. These LR films had a density of edge dislocations close to the combined density of screw and mixed dislocations. The LR films in this study were also found to have a buried conductive layer that is detectable using capacitance-voltage measurements.

  16. Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.

    ERIC Educational Resources Information Center

    Koury, Albert M.; Parcher, Jon F.

    1979-01-01

    Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

  17. Phase-separation induced homogeneous nucleation and growth of Cs{sub 3}LaCl{sub 6} nanoparticles in chalcohalide glass

    SciTech Connect

    Yang, Anping; Lin, Hang; Chen, Daqin; Yu, Yunlong; Wang, Yuansheng

    2014-01-01

    Graphical abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied for the first time. It is experimentally evidenced that the doped active rare earth ions are incorporated into the Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the intensified down- and up-conversion emissions. - Highlights: • A novel transparent glass ceramic containing Cs{sub 3}LaCl{sub 6} nanocrystals was fabricated. • Crystallization behaviors of Cs{sub 3}LaCl{sub 6} nanophase are systematically investigated. • The up-/down-conversion emissions are greatly intensified after crystallization. - Abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied in the GeS{sub 2}-Ga{sub 2}S{sub 3}-La{sub 2}S{sub 3}-LaCl{sub 3}-CsCl system for the first time. Remarkably, the precipitated chloride nanocrystals are spherical and distributed homogeneously in the glass matrix. Benefiting from the uniform structure, high transparency of the glass ceramic is maintained after heat treatment by reducing adverse optical scattering. As revealed by the absorption spectra and Judd–Ofelt calculations, the doped active rare earth ions are partially partitioned into the low-phonon-energy Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the decrease of the non-radiative transition probabilities and therefore intensified photoluminescence emission of Nd{sup 3+} and up-conversion one of Er{sup 3+}.

  18. Dissolution of two-phase microsystems: Gas and liquid microparticle dissolution and dehydration of biomaterials

    NASA Astrophysics Data System (ADS)

    Duncan, Phillip Brent

    A main focus of this research is to develop techniques to study the dissolution process of two-phase microsystems on a single microparticle basis. This dissertation introduces a systematic approach to investigate the formation of microparticles to fulfill the need for rational design of microspheres for a range of applications. This novel method is based on the micropipet manipulation technique and can essentially test any system, where the continuous phase is a liquid and the dispersed phase is practically any phase, a gas (foam), a liquid (emulsion), or a solid (suspension). It is possible to study single microparticle volumes in the picoliter to nanoliter scale, which is on the same size-scale as particles created in bulk suspensions, microsphere processes, and applications. The ability to create, isolate, observe, and manipulate individual gas, liquid or solid microparticles in a well-defined and controlled liquid environment was found to be ideal to study gas microbubbles and microparticles, liquid microdroplets, and the dehydration of dissolved solutes. Subsequently, one can directly measure the dissolution rate and, when a solute is present, calculate its concentration during the dissolution process. Microbubble or microdroplet dissolution in a second phase is driven by two independent factors, a concentration gradient (undersaturation of the dispersed phase in the continuous phase) and a pressure gradient (due to the Laplace-overpressure inside the microparticle created by the surface tension). Experimentally, each of these driving forces can be independently tested. Both the gas microparticle and pure liquid microdroplet dissolution can be predicted by a simple theory based on the diffusion coefficient and solubility limit of the dispersed phase in the continuous phase. The dehydration of a salt ion solution microdroplet results in the nucleation and growth of a crystal, while the dehydration of proteins leads to glassification of the protein. The water remaining in the glassified protein microsphere is on the order of a water monolayer surrounding each protein molecule. Both observation and measurement of dehydration within a single microdroplet is the basis to understanding microparticle formation for use in drug delivery systems and biomolecule preservation.

  19. High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations

    NASA Astrophysics Data System (ADS)

    Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

    1997-11-01

    Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

  20. Geographical and diurnal features of amine-enhanced boundary layer nucleation

    NASA Astrophysics Data System (ADS)

    Bergman, T.; Laaksonen, A.; Korhonen, H.; Malila, J.; Dunne, E. M.; Mielonen, T.; Lehtinen, K. E. J.; Khn, T.; Arola, A.; Kokkola, H.

    2015-09-01

    Amines have recently been found to be an important ingredient in the nucleation and initial growth of atmospheric aerosols; however, global estimates of the spatial and temporal extent of amine-enhanced nucleation are currently missing. We utilize two recently published laboratory data sets of amine-sulfuric acid nucleation to evaluate the accuracy of previously published nucleation parameterizations and to produce a new amine-enhanced new particle formation (NPF) parameterization that better reproduces the laboratory observations at atmospherically relevant sulfuric acid concentrations. We implement and compare the amine-enhanced NPF parameterizations and a kinetic nucleation parameterization within the global aerosol-climate model ECHAM-HAMMOZ and find that the spatial features of amine-enhanced and kinetic NPF are clearly different. Amine-enhanced NPF is limited to areas near the source regions of amine due to its short gas phase residence time of 6.9 h, whereas kinetic nucleation (which depends only on sulfuric acid concentration) produces particles more uniformly across the globe due to long-range transport of SO2. The notably stronger land-sea contrast in amine-enhanced nucleation simulations is in line with relatively rare atmospheric observations of NPF over open oceans. However, when the uptake of gas phase amine molecules to aerosol particles is limited according to previously published estimates (0.2% of collisions leading to uptake), the amine-enhanced NPF parameterization predicts in some regions unrealistically high NPF rates (1000 cm-3 s-1) compared to typical observations. Our results indicate that amine-enhanced nucleation may be an important particle formation mechanism near amine source regions but also highlights the need for more tightly defined constraints on the spatial and temporal distribution of amine emissions, gas-to-particle partitioning mechanisms of amines, and condensation and coagulation sinks in global models.

  1. A dynamic phase-field model for structural transformations and twinning: Regularized interfaces with transparent prescription of complex kinetics and nucleation. Part I: Formulation and one-dimensional characterization

    NASA Astrophysics Data System (ADS)

    Agrawal, Vaibhav; Dayal, Kaushik

    2015-12-01

    The motion of microstructural interfaces is important in modeling twinning and structural phase transformations. Continuum models fall into two classes: sharp-interface models, where interfaces are singular surfaces; and regularized-interface models, such as phase-field models, where interfaces are smeared out. The former are challenging for numerical solutions because the interfaces need to be explicitly tracked, but have the advantage that the kinetics of existing interfaces and the nucleation of new interfaces can be transparently and precisely prescribed. In contrast, phase-field models do not require explicit tracking of interfaces, thereby enabling relatively simple numerical calculations, but the specification of kinetics and nucleation is both restrictive and extremely opaque. This prevents straightforward calibration of phase-field models to experiment and/or molecular simulations, and breaks the multiscale hierarchy of passing information from atomic to continuum. Consequently, phase-field models cannot be confidently used in dynamic settings. This shortcoming of existing phase-field models motivates our work. We present the formulation of a phase-field model - i.e., a model with regularized interfaces that do not require explicit numerical tracking - that allows for easy and transparent prescription of complex interface kinetics and nucleation. The key ingredients are a re-parametrization of the energy density to clearly separate nucleation from kinetics; and an evolution law that comes from a conservation statement for interfaces. This enables clear prescription of nucleation - through the source term of the conservation law - and kinetics - through a distinct interfacial velocity field. A formal limit of the kinetic driving force recovers the classical continuum sharp-interface driving force, providing confidence in both the re-parametrized energy and the evolution statement. We present some 1D calculations characterizing the formulation; in a companion paper, we present more extensive 2D calculations.

  2. Gas phase acetaldehyde production in a continuous bioreactor

    SciTech Connect

    Hwang, Soon Ook . Dept. of Chemical Engineering); Trantolo, D.J. . Center for Biotechnology Engineering); Wise, D.L. . Dept. of Chemical Engineering Northeastern Univ., Boston, MA . Center for Biotechnology Engineering)

    1993-08-20

    The gas phase continuous production of acetaldehyde was studied with particular emphasis on the development of biocatalyst (alcohol oxidase on solid phase support materials) for a fixed bed reactor. Based on the experimental results in a batch bioreactor, the biocatalysts were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, packed into a column, and the continuous acetaldehyde production in the gas phase by alcohol oxidase was performed. The effects of the reaction temperature, flow rates of gaseous stream, and ethanol vapor concentration on the performance of the continuous bioreactor were investigated.

  3. Phase Transition and Fragment Production in the Lattice Gas Model

    NASA Astrophysics Data System (ADS)

    Gulminelli, Francesca; Chomaz, Philippe

    The critical behavior of fragment production is studied within a Lattice Gas Model in the canonical ensemble. Finite size effects on the liquid-gas phase transition are analyzed by a direct calculation of the partition function, and it is shown that phase coexistence and phase transition are relevant concepts even for systems of a few tens of particles. Critical exponents are extracted from the behavior of the fragment production yield as a function of temperature by means of a finite size scaling. The result is that in a finite system well defined critical signals can be found at supercritical (Kertsz line) as well as subcritical densities inside the coexistence zone.

  4. Constant volume gas cell optical phase-shifter

    DOEpatents

    Phillion, Donald W.

    2002-01-01

    A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.

  5. Simulation Approach for Microscale Noncontinuum Gas-Phase Heat Transfer

    NASA Astrophysics Data System (ADS)

    Torczynski, J. R.; Gallis, M. A.

    2008-11-01

    In microscale thermal actuators, gas-phase heat transfer from the heated beams to the adjacent unheated substrate is often the main energy-loss mechanism. Since the beam-substrate gap is comparable to the molecular mean free path, noncontinuum gas effects are important. A simulation approach is presented in which gas-phase heat transfer is described by Fourier's law in the bulk gas and by a wall boundary condition that equates the normal heat flux to the product of the gas-solid temperature difference and a heat transfer coefficient. The dimensionless parameters in this heat transfer coefficient are determined by comparison to Direct Simulation Monte Carlo (DSMC) results for heat transfer from beams of rectangular cross section to the substrate at free-molecular to near-continuum gas pressures. This simulation approach produces reasonably accurate gas-phase heat-transfer results for wide ranges of beam geometries and gas pressures. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  6. Para-Hydrogen-Enhanced Gas-Phase Magnetic Resonance Imaging

    SciTech Connect

    Bouchard, Louis-S.; Kovtunov, Kirill V.; Burt, Scott R.; Anwar,M. Sabieh; Koptyug, Igor V.; Sagdeev, Renad Z.; Pines, Alexander

    2007-02-23

    Herein, we demonstrate magnetic resonance imaging (MRI) inthe gas phase using para-hydrogen (p-H2)-induced polarization. A reactantmixture of H2 enriched in the paraspin state and propylene gas is flowedthrough a reactor cell containing a heterogenized catalyst, Wilkinson'scatalyst immobilized on modified silica gel. The hydrogenation product,propane gas, is transferred to the NMR magnet and is spin-polarized as aresult of the ALTADENA (adiabatic longitudinal transport and dissociationengenders net alignment) effect. A polarization enhancement factor of 300relative to thermally polarized gas was observed in 1D1H NMR spectra.Enhancement was also evident in the magnetic resonance images. This isthe first demonstration of imaging a hyperpolarized gaseous productformed in a hydrogenation reaction catalyzed by a supported catalyst.This result may lead to several important applications, includingflow-through porous materials, gas-phase reaction kinetics and adsorptionstudies, and MRI in low fields, all using catalyst-free polarizedfluids.

  7. Oscillatory burning of solid propellants including gas phase time lag.

    NASA Technical Reports Server (NTRS)

    T'Ien, J. S.

    1972-01-01

    An analysis has been performed for oscillatory burning of solid propellants including gas phase time lag. The gaseous flame is assumed to be premixed and laminar with a one-step overall chemical reaction. The propellant is assumed to decompose according to the Arrenhius Law, with no condensed phase reaction. With this model, strong gas phase resonance has been found in certain cases at the characteristic gas-phase frequencies, but the peaking of the acoustic admittance is in the direction favoring the damping of pressure waves. At still higher frequencies, moderate wave-amplifying ability was found. The limit of low frequency response obtained previously by Denison and Baum was recovered, and the limitations of the quasi-steady theory were investigated.

  8. Evaluation of phase envelope on natural gas, condensate and gas hydrate

    NASA Astrophysics Data System (ADS)

    Promkotra, S.; Kangsadan, T.

    2015-03-01

    The experimentally gas hydrate are generated by condensate and natural gas. Natural gas and condensate samples are collected from a gas processing plant where is situated in the northeastern part of Thailand. Physical properties of the API gravity and density of condensate are presented in the range of 55-60° and 0.71-0.76 g/cm3. The chemical compositions of petroleum-field water are analyzed to evaluate the genesis of gas hydrate by experimental procedure. The hydrochemical compositions of petroleum-field waters are mostly the Na-Cl facies. This condition can estimate how the hydrate forms. Phase envelope of condensate is found only one phase which is liquid phase. The liquid fraction is 100% at 15°C and 101.327 kPa, with the critical pressure and temperature of 2,326 kPa and 611.5 K. However, natural gas can be separated in three phases which are vapor, liquid and solid phase with the pressure and temperature at 100 kPa and 274.2 K. The hydrate curves explicit both hydrate zone and nonhydrate zone. Phase envelope of gas hydrate from the phase diagram indicates the hydrate formation. The experimental results of hydrate form can correlate to the hydrate curve. Besides, the important factor of hydrate formation depends on impurity in the petroleum system.

  9. Substrate orientation effects on the nucleation and growth of the Mn+1AXn phase Ti2AlC

    NASA Astrophysics Data System (ADS)

    Tucker, Mark D.; Persson, Per O. A.˚.; Guenette, Mathew C.; Rosén, Johanna; Bilek, Marcela M. M.; McKenzie, David R.

    2011-01-01

    The Mn+1AXn (MAX) phases are ternary compounds comprising alternating layers of a transition metal carbide or nitride and a third "A-group" element. The effect of substrate orientation on the growth of Ti2AlC MAX phase films was investigated by studying pulsed cathodic arc deposited samples grown on sapphire cut along the (0001), (101¯0), and (11¯02) crystallographic planes. Characterization of these samples was by x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. On the (101¯0) substrate, tilted (101¯8) growth of Ti2AlC was found, such that the TiC octahedra of the MAX phase structure have the same orientation as a spontaneously formed epitaxial TiC sublayer, preserving the typical TiC-Ti2AlC epitaxial relationship and confirming the importance of this relationship in determining MAX phase film orientation. An additional component of Ti2AlC with tilted fiber texture was observed in this sample; tilted fiber texture, or axiotaxy, has not previously been seen in MAX phase films.

  10. Microfabricated Gas Phase Chemical Analysis Systems

    SciTech Connect

    FRYE-MASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; KOTTENSTETTE,RICHARD; LEWIS,PATRICK R.; MANGINELL,RONALD P.; MATZKE,CAROLYN M.; WONG,CHUNGNIN C.

    1999-09-16

    A portable, autonomous, hand-held chemical laboratory ({micro}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

  11. Microfabricated Gas Phase Chemical Analysis Systems

    SciTech Connect

    Casalnuovo, Stephen A.; Frye-Mason, Gregory C; Heller, Edwin J.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carolyn M.; Wong, C. Channy

    1999-08-02

    A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

  12. Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films

    SciTech Connect

    Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

    2008-12-09

    We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

  13. Phase Transition of Methane Gas Hydrate and Response of Marine Gas Hydrate Systems to Environmental Changes

    NASA Astrophysics Data System (ADS)

    Xu, W.

    2003-12-01

    Gas hydrates, which contain mostly methane as the gas component in marine sediment, are stable under relatively high pressure and low temperature conditions such as those found along continental margins and permafrost regions. Its stability is mostly controlled by in-situ pressure, temperature and salinity of pore fluid. Environmentally introduced changes in pressure and temperature can affect the stability of gas hydrate in marine sediment. While certain changes may enhance the process of gas hydrate formation, we are much more interested in the resultant dissociation processes, which may contribute to sub-marine slope instability, seafloor sediment failure, formation of mud volcanoes and pock marks, potential vulnerability of engineering structures, and the risk to drilling and production. We have been developing models to quantify phase transition processes of marine gas hydrates and to investigate the response of marine gas hydrate systems to environmental changes. Methane gas hydrate system is considered as a three-component (water, methane, salt) four-phase (liquid, gas, hydrate, halite) system. Pressure, temperature and salinity of pore fluid constrain the stability of gas hydrate and affect phase transition processes via their effects on methane solubility and fluid density and enthalpy. Compared to the great quantity of studies on its stability in the literature, in-depth research on phase transition of gas hydrate is surprisingly much less. A method, which employs pressure, enthalpy, salinity and methane content as independent variables, is developed to calculate phase transition processes of the three-component four-phase system. Temperature, an intensive thermodynamic parameter, is found not sufficient in describing phase transition of gas hydrate. The extensive thermodynamic parameter enthalpy, on the other hand, is found to be sufficient both in calculation of the phase transition processes and in modeling marine gas hydrate systems. Processes considered in this study to introduce gas hydrate dissociation in marine sediment include sedimentation, sea level drop and increasing seafloor temperature. Calculations indicate that dissociation of gas hydrates may lead to a build-up of excess pore pressure in marine sediment. The most significant factor constraining the magnitude of over-pressure is sediment permeability. The rate of sedimentation and pressure or temperature change at seafloor affects the degree and rate of gas hydrate dissociation and, hence, also the degree of excess pore pressure. The relationship between gas hydrate dissociation and the stability/failure of marine sediment are to be further discussed.

  14. Development and evaluation of the aerosol dynamic and gas phase chemistry model ADCHEM

    NASA Astrophysics Data System (ADS)

    Roldin, P.; Swietlicki, E.; Schurgers, G.; Arneth, A.; Lehtinen, K. E. J.; Boy, M.; Kulmala, M.

    2010-08-01

    The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (11 km2) to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM), which has been developed and used at Lund University since 2007. The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions), which is not treated in Lagrangian box-models (0-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others ideally suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The gas phase chemistry model calculates the gas phase concentrations of 63 different species, using 119 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malm in Southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, coupled or uncoupled condensation, the volatility basis set (VBS) or traditional 2-product model for secondary organic aerosol formation, different aerosol dynamic processes and vertical and horizontal mixing. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malm is mainly affected by dry deposition, coagulation and condensation, and is relatively insensitive to moderate variations in the vertical and horizontal mixing, as long as the mixing height is relatively uniform. The modeled PM2.5 was dominated by organics, nitrate, sulfate and ammonium. If treating the condensation of HNO3 and NH3 as a coupled process (pH independent) the model gave lower nitrate PM2.5 values than if considering uncoupled condensation. However, both methods gave similar and significant temporal variation in the particulate nitrate content, primarily due to fluctuation in the relative humidity.

  15. Collision-induced gas phase dissociation rates

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1990-01-01

    The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

  16. Gas and aqueous phase measurements of hydrogen peroxide

    SciTech Connect

    Kok, G.L.; Heikes, B.G.; Lazrus, A.L.

    1986-04-01

    In the past several years, a great deal of effort has been put forth to develop techniques for the determination of atmospheric H/sub 2/O/sub 2/. Presently, there is one technique known to be available for the determination of H/sub 2/O/sub 2/ in both the gas and aqueous phases. This technique relies on the enzyme catalyzed dimerization of p-hydroxyphenylacetic acid in the presence of H/sub 2/O/sub 2/. The reaction takes place in the aqueous phase and the dimer is quantitated using fluorescence techniques. For the determination of H/sub 2/O/sub 2/ in the aqueous phase, this technique has a detection limit of 1 x 10/sup -8/ M. Adapting the same analytical procedure with an inlet system which provides for the pre-concentration of gas-phase H/sub 2/O/sub 2/ in water a detection limit of 50 pptb is obtained. Two additional techniques are known for the determination of either gas or aqueous phase H/sub 2/O/sub 2/. A tunable diode laser absorption system (TDLAS) is under development for the determination of H/sub 2/O/sub 2/ in the gas-phase. A technique employing the chemiluminescent oxidation of oxalic acid esters by H/sub 2/O/sub 2/ has been developed and is in operation for the determination of aqueous-phase H/sub 2/O/sub 2/. An interlaboratory comparison between the fluorescence technique and the TDLAS system for gas-phase indicated good agreement between the methods. Comparison of the fluorescence and chemiluminescent techniques for aqueous H/sub 2/O/sub 2/ using laboratory standards and ambient samples indicated no significant bias in either technique.

  17. Capillary gas chromatography with two new moderately high temperature phases.

    NASA Technical Reports Server (NTRS)

    Pollock, G. E.

    1972-01-01

    Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

  18. Exxon gains gas-phase patent, makes LLDPE

    SciTech Connect

    Rotman, D.

    1995-04-26

    Exxon chemical says it has made linear low-density polyethylene (LLDPE) using metallocene catalysts at its world-scale gas-phase plant in Mont Belvieu, TX. Exxon also says it has received a broad US patent that covers the use of metallocenes in gas-phase reactors that use condensing mode technology and that it plans to license the know-how. The moves, say industry experts, greatly strengthen Exxon`s position in metallocenes, particularly in pushing metallocene-based PE into commodity markets. The use of gas-phase technology {open_quotes}had to happen{close_quotes} to allow metallocene polymers to compete as commodities, says David Highfield, v.p. at Catalyst Consultants (Spring House, PA). {open_quotes}It`s very important and very significant in widening the scope of [metallocene] technology.{close_quotes}

  19. Effect of phase behavior on bypassing in enriched gas floods

    SciTech Connect

    Burger, J.E.; Bhogeswara, R.; Mohanty, K.K. )

    1994-05-01

    Enriched gas floods incorporate a complex interaction of heterogeneity, fingering, multiphase flow, and phase behavior. Experiments and simulations indicate that the optimum solvent enrichment in high-viscosity-ratio secondary gas floods can be below minimum miscibility enrichment (MME). The compositional path and resulting mobility profile in multidimensional multiple-contact miscible (MCM) or immiscible floods are different from their 1D counterparts for high-viscosity-ratio floods in heterogeneous media.

  20. Freeze drying for gas chromatography stationary phase deposition

    DOEpatents

    Sylwester, Alan P.

    2007-01-02

    The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

  1. Gas phase chemical detection with an integrated chemical analysis system

    SciTech Connect

    CASALNUOVO,STEPHEN A.; FRYE-MASON,GREGORY CHARLES; KOTTENSTETTE,RICHARD; HELLER,EDWIN J.; MATZKE,CAROLYN M.; LEWIS,PATRICK R.; MANGINELL,RONALD P.; BACA,ALBERT G.; HIETALA,VINCENT M.

    2000-04-12

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.

  2. Negative ion gas-phase chemistry of arenes.

    PubMed

    Danikiewicz, Witold; Zimnicka, Magdalena

    2016-01-01

    Reactions of aromatic and heteroaromatic compounds involving anions are of great importance in organic synthesis. Some of these reactions have been studied in the gas phase and are occasionally mentioned in reviews devoted to gas-phase negative ion chemistry, but no reviews exist that collect all existing information about these reactions. This work is intended to fill this gap. In the first part of this review, methods for generating arene anions in the gas phase and studying their physicochemical properties and fragmentation reactions are presented. The main topics in this part are as follows: processes in which gas-phase arene anions are formed, measurements and calculations of the proton affinities of arene anions, proton exchange reactions, and fragmentation processes of substituted arene anions, especially phenide ions. The second part is devoted to gas-phase reactions of arene anions. The most important of these are reactions with electrophiles such as carbonyl compounds and ?,?-unsaturated carbonyl and related compounds (Michael acceptors). Other reactions including oxidation of arene anions and halogenophilic reactions are also presented. In the last part of the review, reactions of electrophilic arenes with nucleophiles are discussed. The best known of these is the aromatic nucleophilic substitution (SN Ar) reaction; however, other processes that lead to the substitution of a hydrogen atom in the aromatic ring are also very important. Aromatic substrates in these reactions are usually but not always nitroarenes bearing other substituents in the ring. The first step in these reactions is the formation of an anionic ?-adduct, which, depending on the substituents in the aromatic ring and the structure of the attacking nucleophile, is either an intermediate or a transition state in the reaction path. In the present review, we attempted to collect the results of both experimental and computational studies of the aforementioned reactions conducted since the very beginning of gas-phase negative ion chemistry. 2015 Wiley Periodicals, Inc. Mass Spec Rev 35: 123-146, 2016. PMID:25851641

  3. Analysis of the gas phase reactivity of chlorosilanes.

    PubMed

    Ravasio, Stefano; Masi, Maurizio; Cavallotti, Carlo

    2013-06-27

    Trichlorosilane is the most used precursor to deposit silicon for photovoltaic applications. Despite of this, its gas phase and surface kinetics have not yet been completely understood. In the present work, it is reported a systematic investigation aimed at determining what is the dominant gas phase chemistry active during the chemical vapor deposition of Si from trichlorosilane. The gas phase mechanism was developed calculating the rate constant of each reaction using conventional transition state theory in the rigid rotor-harmonic oscillator approximation. Torsional vibrations were described using a hindered rotor model. Structures and vibrational frequencies of reactants and transition states were determined at the B3LYP/6-31+G(d,p) level, while potential energy surfaces and activation energies were computed at the CCSD(T) level using aug-cc-pVDZ and aug-cc-pVTZ basis sets extrapolating to the complete basis set limit. As gas phase and surface reactivities are mutually interlinked, simulations were performed using a microkinetic surface mechanism. It was found that the gas phase reactivity follows two different routes. The disilane mechanism, in which the formation of disilanes as reaction intermediates favors the conversion between the most stable monosilane species, and the radical pathway, initiated by the decomposition of Si2HCl5 and followed by a series of fast propagation reactions. Though both mechanisms are active during deposition, the simulations revealed that above a certain temperature and conversion threshold the radical mechanism provides a faster route for the conversion of SiHCl3 into SiCl4, a reaction that favors the overall Si deposition process as it is associated with the consumption of HCl, a fast etchant of Si. Also, this study shows that the formation of disilanes as reactant intermediates promotes significantly the gas phase reactivity, as they contribute both to the initiation of radical chain mechanisms and provide a catalytic route for the conversion between the most stable monosilanes. PMID:23731215

  4. Gas purification in the dense phase at the CATS terminal

    SciTech Connect

    Openshaw, P.J.; Carnell, P.J.H.; Rhodes, E.F.

    1999-07-01

    The purification and transportation of natural gas at very high pressures can help to minimize the capital cost of pipelines and processing equipment. However, complex mixtures of hydrocarbons undergo unusual phase changes, such as retrograde condensation, as the temperature and pressure are altered. The Central Area Transmission System (CATS) is a joint venture of Amoci, BG, Amerada Hess, Phillips, Agip and Fina operated by Amoco on behalf of the owners. The design of the CATS terminal has provided an interesting processing challenge. The terminal receives a total of 1.6 Bscf/d of rich gas from a number of offshore fields. All are relatively sweet but the small amounts of H{sub 2}S and Hg are removed. Fixed bed technology was selected as the most economic purification process, while minimizing hydrocarbon loss and operator involvement. Conventionally, the raw gas would be split into the different hydrocarbon fractions and each would be processed separately. This would require the installation of a large number of reactors. A more elegant solution is to treat the gas on arrival at the terminal in the dense phase. This option raised questions around whether a fixed bed would be prone to fouling, could the pressure drop be kept low enough to avoid phase separation and would inadvertent wetting by condensation cause problems. Details are given of the test work carried out to prove the viability of using fixed bed technology for dense phase gas processing, the eventual design adopted and the performance over the first year of service.

  5. Fabrication and morphologies of large directly ordered L1{sub 0} FePt nanoparticles in gas phase

    SciTech Connect

    Liu Xiaoqi; Wang Jianping

    2009-04-01

    Gas phase synthesis of large directly ordered L1{sub 0} FePt nanoparticles was studied. Simultaneous control of the chemical ordering and the size of the FePt nanoparticle was successfully achieved. It was found that the chemical ordering of the FePt nanoparticles was mainly influenced by the energy conditions (thermal environments at nucleation and growth regions), which could be adjusted by varying the process parameters including the sputtering current density, the Ar gas pressure, etc. The sizes of ordered FePt nanoparticles were more related to the Fe and Pt atoms' density at the initial stage (close to target surface). Multiply twinned structures were observed in L1{sub 0} FePt nanoparticles with 12 and 17 nm mean sizes, but were absent in L1{sub 0} FePt nanoparticles with 6 nm mean size, which caused the relatively low coercivity of large L1{sub 0} FePt nanoparticles.

  6. Calculation of two-phase flow in gas turbine combustors

    SciTech Connect

    Tolpadi, A.K.

    1995-10-01

    A method is presented for computing steady two-phase turbulent combusting flow in a gas turbine combustor. The gas phase equations are solved in an Eulerian frame of reference. The two-phase calculations are performed by using a liquid droplet spray combustion a model and treating the motion of the evaporating fuel droplets in a Lagrangian frame of reference. The numerical algorithm employs nonorthogonal curvilinear coordinates, a multigrid iterative solution procedure, the standard k-{epsilon} turbulence model, and a combustion model comprising an assumed shape probability density function and the conserved scalar formulation. The trajectory computation of the fuel provides the source terms for all the gas phase equations. This two-phase model was applied to a real piece of combustion hardware in the form of a modern GE/SNECMA single annular CFM56 turbofan engine combustor. For the purposes of comparison, calculations were also performed by treating the fuel as a single gaseous phase. The effect on the solution of two extreme situations of the fuel as a gas and initially as a liquid was examined. The distribution of the velocity field and the conserved scalar within the combustor, as well as the distribution of the temperature field in the reaction zone and in the exhaust, were all predicted with the combustor operating both at high-power and low-power (ground idle) conditions. The calculated exit gas temperature was compared with test rig measurements. Under both low and high-power conditions, the temperature appeared to show an improved agreement with the measured data when the calculations were performed with the spray model as compared to a single-phase calculation.

  7. Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors.

    PubMed

    Zang, Yaping; Zhang, Fengjiao; Huang, Dazhen; Di, Chong-an; Meng, Qing; Gao, Xike; Zhu, Daoben

    2014-05-01

    Utilizing a textbook reaction on the surface of an organic active channel, achieves sensitive detection of HCl, NH3 and NO2, with good selectivity, excellent reproducibility, and satisfactory stability. These results reveal gas-phase reaction assisted detection as a unique and promising approach to construct practical applicable gas sensors with typical organic transistors. PMID:24510689

  8. Gas phase radiative effects in diffusion flames

    NASA Astrophysics Data System (ADS)

    Bedir, Hasan

    Several radiation models are evaluated for a stagnation point diffusion flame of a solid fuel in terms of accuracy and computational time. Narrowband, wideband, spectral line weighted sum of gray gases (SLWSGG), and gray gas models are included in the comparison. Radiative heat flux predictions by the nongray narrowband, wideband, and SLWSGG models are found to be in good agreement with each other, whereas the gray gas models are found to be inaccurate. The narrowband model, the most complex among the models evaluated, is then applied first to a solid fuel and second to a pure gaseous diffusion flame. A polymethylmethacrylate (PMMA) diffusion flame in a stagnation point geometry is solved with the narrowband model with COsb2, Hsb2O, and MMA vapor included in participating species. A detailed account of the emission and absorption from these species as well as the radiative heat fluxes are given as a function of the stretch rate. It is found that at low stretch rate the importance of radiation is increased due to an increase in the optical thickness, and a decrease in the conductive heat flux. Results show that COsb2 is the biggest emitter and absorber in the flame, MMA vapor is the second and Hsb2O is the least important. A pure gaseous flame in an opposed jet configuration is solved with the narrowband radiation model with CO as the fuel, and Osb2 as the oxidizer. Detailed. chemical kinetics and transport are incorporated into the combustion model with the use of the CHEMKIN and TRANSPORT software packages. The governing equations are solved with a modified version of the OPPDIF code. Dry and wet CO flames as well as COsb2 dilution are studied. Comparison of the results with and without the consideration of radiation reveals that the radiation is important for the whole flammable range of dry CO flames and for the low stretch rates of wet flames. Without the consideration of radiation the temperature and the species mole fractions (especially of minor species) predictions are different in comparison to the results with the inclusion of the radiation in the model. A flammability map with added Hsb2O fraction and stretch rate as coordinates is drawn. The flammability map contains a blow off extinction boundary at high stretch rate and a quenching extinction boundary at low stretch rate. With increasing Hsb2O addition the quenching boundary shifts to lower stretch rates and the blow off boundary shifts to higher stretch rates, hence the range of flammable stretch rates increases. COsb2 dilution of the fuel (CO) jet is found to decrease the flame temperature. A flammability map with COsb2 mole fraction in the fuel jet and the stretch rate as coordinates is also drawn. With increasing COsb2 dilution the range of flammable stretch rate decreases. For the dry CO-Osb2 case, when COsb2 dilution exceeds 17%, the system is nonflammable for any stretch rate. The most flammable stretch rate is around 2 ssp{-1}.

  9. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    2003-01-01

    By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

  10. Rupture of the cell envelope by induced intracellular gas phase expansion in gas vacuolate bacteria.

    PubMed Central

    Hemmingsen, B B; Hemmingsen, E A

    1980-01-01

    Using a new approach, we estimated the physical strength of the cell envelopes of three species of gram-negative, gas vacuolate bacteria (Microcyclus aquaticus, Prosthecomicrobium pneumaticum, and Meniscus glaucopis). Populations of cells were slowly (0.5 to 2.9 h) saturated with argon, nitrogen, or helium to final pressures up to 100 atm (10, 132 kPa). The gas phases of the vesicles remained intact and, upon rapid (1 to 2 s) decompression to atmospheric pressure, expanded and ruptured the cells; loss of colony-forming units was used as an index of rupture. Because the cell envelope is the cellular component most likely to resist the expanding intracellular gas phase, its strength can be estimated from the minimum gas pressures that produce rupture. The viable counts indicated that these minimum pressures were between 25 and 50 atm; the majority of the cell envelopes were ruptured at pressures between 50 and 100 atm. Cells in which the gas vesicles were collapsed and the gas phases were effectively dissolved by rapid compression tolerated decompression from much higher gas saturations. Cells that do not normally possess gas vesicles (Escherichia coli) or that had been prevented from forming them by addition of L-lysine to the medium (M. aquaticus) were not harmed by decompression from gas saturation pressures up to 300 atm. PMID:7204336

  11. Nucleation and growth of Ag nanoparticles on amorphous carbon surface from vapor phase formed by vacuum evaporation

    NASA Astrophysics Data System (ADS)

    Gromov, Dmitry G.; Pavlova, Lydia M.; Savitsky, Andrey I.; Trifonov, Alexey Yu.

    2015-03-01

    We present the results of experimental study of Ag nanoparticle arrays on thin film of amorphous carbon. The arrays were formed by means of vapor phase deposition on non-heated substrate. The investigation was carried out using TEM technique. It has been found that the size of the particles and their surface density significantly depend on the amount of condensing substance. In particular, increasing the portion of evaporating Ag material from 5.1 to 47.5 mg results in drastic reduction of surface density of the particles from ~8,000 to ~40 m-2, whereas the predominant particle size changes from ~7 to ~60 nm. We present phenomenological description of the process: directed flow of silver atoms to growing Ag particles takes place during condensation.

  12. Nucleation and growth of Ag islands on the (.sqroot.3 × .sqroot.3)R30° phase of Ag on Si(111)

    SciTech Connect

    Belianinov, A.; Unal, B.; Ho, K.-M.; Wang, C.-Z.; Evans, J. W.; Tringides, M. C.; Thiel, P. A.

    2011-06-06

    We use scanning tunneling microscopy to measure densities and characteristics of Ag islands that form on the ({radical}3 x {radical}3)R30{sup o}-Ag phase on Si(111), as a function of deposition temperature. Nucleation theory predicts that the logarithm of island density varies linearly with inverse deposition temperature. The data show two linear regimes. At 50-125 K, islands are relatively small, and island density decreases only slightly with increasing temperature. At 180-250 K, islands are larger and polycrystalline, and island density decreases strongly with increasing temperature. At 300 K, Ag atoms can travel for distances of the order of 1 {micro}m. Assuming that Ag diffusion occurs via thermally activated motion of single atoms between adjacent sites, the data can be explained as follows. At 50-125 K, the island density does not follow conventional Arrhenius scaling due to limited mobility and a consequent breakdown of the steady-state condition for the adatom density. At {approx} 115-125 K, a transition to conventional Arrhenius scaling with critical nucleus size (i = 1) begins, and at 180-250 K, i > 1 prevails. The transition points indicate a diffusion barrier of 0.20-0.23 eV and a pairwise Ag-Ag bond strength of 0.14 eV. These energy values lead to an estimate of i {approx} 3-4 in the regime 180-250 K, where island density varies strongly with temperature.

  13. Investigation of condensed and early stage gas phase hypergolic reactions

    NASA Astrophysics Data System (ADS)

    Dennis, Jacob Daniel

    Traditional hypergolic propellant combinations, such as those used on the space shuttle orbital maneuvering system first flown in 1981, feature hydrazine based fuels and nitrogen tetroxide (NTO) based oxidizers. Despite the long history of hypergolic propellant implementation, the processes that govern hypergolic ignition are not well understood. In order to achieve ignition, condensed phase fuel and oxidizer must undergo simultaneous physical mixing and chemical reaction. This process generates heat, intermediate condensed phase species, and gas phase species, which then may continue to react and generate more heat until ignition is achieved. The process is not well understood because condensed and gas phase reactions occur rapidly, typically in less than 200 ?s, on much faster timescales than traditional diagnostic methods can observe. A detailed understanding of even the gas phase chemistry is lacking, but is critical for model development. Initial research has provided confidence that a study of condensed phase hypergolic reactions is useful and possible. Results obtained using an impinging jet apparatus have shown a critical residence time of 0.3 ms is required for the reaction between monomethylhydrazine (MMH) and red fuming nitric acid (RFNA, ~85% HNO3 + 15% N2O4) to achieve conditions favorable for ignition. This critical residence time spans the time required for liquid phase reactions to occur at the fuel/oxidizer interface and can give some insight into the reaction rates for this propellant combination. Experiments performed in a forced mixing constant volume reactor have demonstrated that the chamber pressurization rate for MMH/RFNA can be significantly reduced by diluting the MMH with deionized water. This result indicates that propellant dilution can slow the chemical reaction rates to occur over observable time scales. The research described in this document consists of two efforts that contribute knowledge to the propulsion community regarding the hypergolic liquid propellant combination of MMH and RFNA or pure nitric acid. The first and most important effort focuses on furthering the understanding of condensed phase reactions between MMH and nitric acid. To accomplish this goal diluted MMH and nitric acid were studied in a Fourier transform infrared spectrometer. By tracking the generation or destruction of specific chemical species in the reacting fluid we can measure the reaction progress as a function of reactant concentration and temperature. This work provides the propulsion community with a quantitative global condensed phase reaction rate equation for MMH/nitric acid. The second effort focuses on improving understanding the recently proposed gas phase hypergolic reaction mechanisms using a streak camera based ultraviolet and visible spectrometer. The time resolution on the streak camera system allows for detailed investigation of the pre-ignition and early stage gas phase species present during the reaction between MMH and RFNA.

  14. Characterizing protein crystal nucleation

    NASA Astrophysics Data System (ADS)

    Akella, Sathish V.

    We developed an experimental microfluidic based technique to measure the nucleation rates and successfully applied the technique to measure nucleation rates of lysozyme crystals. The technique involves counting the number of samples which do not have crystals as a function of time. Under the assumption that nucleation is a Poisson process, the fraction of samples with no crystals decays exponentially with the decay constant proportional to nucleation rate and volume of the sample. Since nucleation is a random and rare event, one needs to perform measurements on large number of samples to obtain good statistics. Microfluidics offers the solution of producing large number of samples at minimal material consumption. Hence, we developed a microfluidic method and measured nucleation rates of lysozyme crystals in supersaturated protein drops, each with volume of ˜ 1 nL. Classical Nucleation Theory (CNT) describes the kinetics of nucleation and predicts the functional form of nucleation rate in terms of the thermodynamic quantities involved, such as supersaturation, temperature, etc. We analyzed the measured nucleation rates in the context of CNT and obtained the activation energy and the kinetic pre-factor characterizing the nucleation process. One conclusion is that heterogeneous nucleation dominates crystallization. We report preliminary studies on selective enhancement of nucleation in one of the crystal polymorprhs of lysozyme (spherulite) using amorphous mesoporous bioactive gel-glass te{naomi06, naomi08}, CaO.P 2O5.SiO2 (known as bio-glass) with 2-10 nm pore-size diameter distribution. The pores act as heterogeneous nucleation centers and claimed to enhance the nucleation rates by molecular confinement. The measured kinetic profiles of crystal fraction of spherulites indicate that the crystallization of spherulites may be proceeding via secondary nucleation pathways.

  15. Molecular dynamics of simulation of the nucleation, growth, inhibition and control of gas hydrates. Annual report, March 1992-June 1993

    SciTech Connect

    Clancy, P.

    1993-06-01

    This is the second year of a three-year project using molecular simulation techniques tailored specifically for the determination of early-stage kinetics of natural gas hydrate crystal growth and dissolution. This year, extensive simulations of the kinetics of growth of a model system showed the appearance of magic numbers' in the growth rate versus cluster size. The feasibility of monitoring the kinetics of hydrate growth and dissolution has been demonstrated. A preliminary mechanism for hydrate dissolution has been proposed. A building block' for hydrate growth has been identified as a long-lived entity in the liquid; this single dodecahedron has also been seen by preliminary NMR studies. Inhibition studies have begun with biopolymers and will continue next year with studies of simple inhibitors, in concert with molecular spectroscopic techniques.

  16. Studies in Three Phase Gas-Liquid Fluidised Systems

    NASA Astrophysics Data System (ADS)

    Awofisayo, Joyce Ololade

    1992-01-01

    Available from UMI in association with The British Library. The work is a logical continuation of research started at Aston some years ago when studies were conducted on fermentations in bubble columns. The present work highlights typical design and operating problems that could arise in such systems as waste water, chemical, biochemical and petroleum operations involving three-phase, gas-liquid -solid fluidisation; such systems are in increasing use. It is believed that this is one of few studies concerned with "true" three-phase, gas-liquid-solid fluidised systems, and that this work will contribute significantly to closing some of the gaps in knowledge in this area. The research work was experimentally based and involved studies of the hydrodynamic parameters, phase holdups (gas and solid), particle mixing and segregation, and phase flow dynamics (flow regime and circulation patterns). The studies have focused particularly on the solid behaviour and the influence of properties of solids present on the above parameters in three-phase, gas-liquid-solid fluidised systems containing single particle components and those containing binary and ternary mixtures of particles. All particles were near spherical in shape and two particle sizes and total concentration levels were used. Experiments were carried out in two- and three-dimensional bubble columns. Quantitative results are presented in graphical form and are supported by qualitative results from visual studies which are also shown as schematic diagrams and in photographic form. Gas and solid holdup results are compared for air-water containing single, binary and ternary component particle mixtures. It should be noted that the criteria for selection of the materials used are very important if true three-phase fluidisation is to be achieved: this is very evident when comparing the results with those in the literature. The fluid flow and circulation patterns observed were assessed for validation of the generally accepted patterns, and the author believes that the present work provides more accurate insight into the modelling of liquid circulation in bubble columns. The characteristic bubbly flow at low gas velocity in a two-phase system is suppressed in the three-phase system. The degree of mixing within the system is found to be dependent on flow regime, liquid circulation and the ratio of solid phase physical properties.

  17. Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments

    NASA Astrophysics Data System (ADS)

    He, J.; Zhang, Y.

    2014-09-01

    Gas-phase chemistry and subsequent gas-to-particle conversion processes such as new particle formation, condensation, and thermodynamic partitioning have large impacts on air quality, climate, and public health through influencing the amounts and distributions of gaseous precursors and secondary aerosols. Their roles in global air quality and climate are examined in this work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a 7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical homogenous nucleation (binary and ternary) and activation nucleation (empirical first-order power law) parameterizations, and a highly simplified inorganic aerosol thermodynamics treatment that only simulates particulate-phase sulfate and ammonium. In this work, a new gas-phase chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global Extension (CB05_GE) and several advanced inorganic aerosol treatments for condensation of volatile species, ion-mediated nucleation (IMN), and explicit inorganic aerosol thermodynamics for sulfate, ammonium, nitrate, sodium, and chloride have been incorporated into CESM/CAM5.1-MAM7. Compared to the simple gas-phase chemistry, CB05_GE can predict many more gaseous species, and thus could improve model performance for PM2.5, PM10, PM components, and some PM gaseous precursors such as SO2 and NH3 in several regions as well as aerosol optical depth (AOD) and cloud properties (e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and shortwave cloud forcing, SWCF) on the global scale. The modified condensation and aqueous-phase chemistry could further improve the prediction of additional variables such as HNO3, NO2, and O3 in some regions, and new particle formation rate (J) and AOD on the global scale. IMN can improve the prediction of secondary PM2.5 components, PM2.5, and PM10 over Europe as well as AOD and CDNC on the global scale. The explicit inorganic aerosol thermodynamics using the ISORROPIA II model improves the prediction of all major PM2.5 components and their gaseous precursors in some regions as well as downwelling shortwave radiation, SWCF, and cloud condensation nuclei at a supersaturation of 0.5% on the global scale. For simulations of 2001-2005 with all the modified and new treatments, the improved model predicts that on global average, SWCF increases by 2.7 W m-2, reducing the normalized mean bias (NMB) of SWCF from -5.4 to 1.2%. Uncertainties in emissions can largely explain the inaccurate prediction of precursor gases (e.g., SO2, NH3, and NO) and primary aerosols (e.g., black carbon and primary organic matter). Additional factors leading to the discrepancies between model predictions and observations include assumptions associated with equilibrium partitioning for fine particles assumed in ISORROPIA II, irreversible gas/particle mass transfer treatment for coarse particles, uncertainties in model treatments such as dust emissions, secondary organic aerosol formation, multi-phase chemistry, cloud microphysics, aerosol-cloud interaction, dry and wet deposition, and model parameters (e.g., accommodation coefficients and prefactors of the nucleation power law) as well as uncertainties in model configuration such as the use of a coarse-grid resolution.

  18. EVALUATION OF THE GAS-PHASE CHEMICAL MECHANISM

    EPA Science Inventory

    A program was conducted to evaluate the gas-phase mechanism developed for the Regional Acid Deposition Model (RADM). n initial review of the mechanism was carried out, resulting in several modifications being made prior to its further evaluation. ew methods were developed for pro...

  19. Selected Examples of Gas-Phase Ion Chemistry Studies

    PubMed Central

    Nibbering, Nico M. M.

    2013-01-01

    Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Trger bases having chiral nitrogen centers. PMID:24349921

  20. LOW COST IMAGER FOR POLLUTANT GAS LEAK DETECTION - PHASE II

    EPA Science Inventory

    An inexpensive imaging Instrument to quickly locate leaks of methane and other greenhouse and VOC gases would reduce the cost and effort expended by industry to comply with EPA regulations. In Phase I, of this WBIR program, a new gas leak visualization camera was demonstrated...

  1. Ion-Molecule Reactions in Gas Phase Radiation Chemistry.

    ERIC Educational Resources Information Center

    Willis, Clive

    1981-01-01

    Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

  2. INVESTIGATION OF GAS-PHASE OZONE AS A POTENTIAL BIOCIDE

    EPA Science Inventory

    The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...

  3. Nucleation of copper during supersonic expansion

    SciTech Connect

    Ahluwalia, R.K.; Im, K.H.

    1989-12-01

    Nucleation of copper vapor during gas expansion in a supersonic nozzle is investigated. Time scales for nucleation delay and supersaturation doubling are considered in establishing the need for non-steady state nucleation theory. A population balance model is constructed for tracking the size spectrum of stable clusters formed from self nucleation and exposed to supersaturated gas. It is found that at average cooling rates exceeding 10{sup 7} K/s, copper vapor exists in a highly nonequilibrium concentration at the nozzle exit. Copper condensation is severely limited by the nucleation kinetics and the available residence time. It is influenced by the monomer concentration and the nozzle exit pressure and temperature. The size spectrum of stable clusters is dominated by small clusters containing fewer than fifteen molecules. Nucleation persists throughout the expansion process because of the inability of the vapor condensation processes to relieve supersaturation buildup due to rapid gas cooling. Nucleation rate is sensitive to the surface energy of the clusters corresponding to the critical size. Monte-Carlo simulations of admissible cluster configurations are recommended for determining statistically-averaged surface energies of clusters containing two-to-twenty molecules. 7 refs., 10 figs., 6 tabs.

  4. Realization of an excited, strongly correlated quantum gas phase.

    PubMed

    Haller, Elmar; Gustavsson, Mattias; Mark, Manfred J; Danzl, Johann G; Hart, Russell; Pupillo, Guido; Ngerl, Hanns-Christoph

    2009-09-01

    Ultracold atomic physics offers myriad possibilities to study strongly correlated many-body systems in lower dimensions. Typically, only ground-state phases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we realized and controlled in one-dimensional geometry a highly excited quantum phase that is stabilized in the presence of attractive interactions by maintaining and strengthening quantum correlations across a confinement-induced resonance. We diagnosed the crossover from repulsive to attractive interactions in terms of the stiffness and energy of the system. Our results open up the experimental study of metastable, excited, many-body phases with strong correlations and their dynamical properties. PMID:19729651

  5. Electrochemical Nucleation of Stable N2 Nanobubbles at Pt Nanoelectrodes.

    PubMed

    Chen, Qianjin; Wiedenroth, Hilke S; German, Sean R; White, Henry S

    2015-09-23

    Exploring the nucleation of gas bubbles at interfaces is of fundamental interest. Herein, we report the nucleation of individual N2 nanobubbles at Pt nanodisk electrodes (6–90 nm) via the irreversible electrooxidation of hydrazine (N2H4 → N2 + 4H(+) + 4e(–)). The nucleation and growth of a stable N2 nanobubble at the Pt electrode is indicated by a sudden drop in voltammetric current, a consequence of restricted mass transport of N2H4 to the electrode surface following the liquid-to-gas phase transition. The critical surface concentration of dissolved N2 required for nanobubble nucleation, CN2,critical(s), obtained from the faradaic current at the moment just prior to bubble formation, is measured to be ∼0.11 M and is independent of the electrode radius and the bulk N2H4 concentration. Our results suggest that the size of stable gas bubble nuclei depends only on the local concentration of N2 near the electrode surface, consistent with previously reported studies of the electrogeneration of H2 nanobubbles. CN2,critical(s) is ∼160 times larger than the N2 saturation concentration at room temperature and atmospheric pressure. The residual current for N2H4 oxidation after formation of a stable N2 nanobubble at the electrode surface is proportional to the N2H4 concentration as well as the nanoelectrode radius, indicating that the dynamic equilibrium required for the existence of a stable N2 nanobubble is determined by N2H4 electrooxidation at the three phase contact line. PMID:26322525

  6. Flavin Adenine Dinucleotide Structural Motifs: From Solution to Gas Phase

    PubMed Central

    2015-01-01

    Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H]+ and [M + Na]+molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a stack to a close conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the solvation effect created with the organic molecules. PMID:25222439

  7. Gas-phase chemistry of ruthenium and rhodium carbonyl complexes.

    PubMed

    Cao, Shiwei; Wang, Yang; Qin, Zhi; Fan, Fangli; Haba, Hiromitsu; Komori, Yukiko; Wu, Xiaolei; Tan, Cunmin; Zhang, Xin

    2016-01-01

    Short-lived ruthenium and rhodium isotopes were produced from a (252)Cf spontaneous fission (SF) source. Their volatile carbonyl complexes were formed in gas-phase reactions in situ with the carbon-monoxide containing gas. A gas-jet system was employed to transport the volatile carbonyls from the recoil chamber to the chemical separation apparatus. The gas-phase chemical behaviors of these carbonyl complexes were studied using an online low temperature isothermal chromatography (IC) technique. Long IC columns made up of FEP Teflon were used to obtain the chemical information of the high-volatile Ru and Rh carbonyls. By excluding the influence of precursor effects, short-lived isotopes of (109-110)Ru and (111-112)Rh were used to represent the chemical behaviours of Ru and Rh carbonyls. Relative chemical yields of about 75% and 20% were measured for Ru(CO)5 and Rh(CO)4, respectively, relative to the yields of KCl aerosols transported in Ar gas. The adsorption enthalpies of ruthenium and rhodium carbonyl complexes on a Teflon surface were determined to be around ΔHads = -33 kJ mol(-1) and -36 kJ mol(-1), respectively, by fitting the breakthrough curves of the corresponding carbonyl complexes with a Monte Carlo simulation program. Different from Mo and Tc carbonyls, a small amount of oxygen gas was found to be not effective for the chemical yields of ruthenium and rhodium carbonyl complexes. The general chemical behaviors of short-lived carbonyl complexes of group VI-IX elements were discussed, which can be used in the future study on the gas-phase chemistry of superheavy elements - Bh, Hs, and Mt carbonyls. PMID:26573993

  8. Liquid-gas phase transition in nuclear matter including strangeness

    SciTech Connect

    Wang, P.; Leinweber, D.B.; Williams, A.G.; Thomas, A.W.

    2004-11-01

    We apply the chiral SU(3) quark mean field model to study the properties of strange hadronic matter at finite temperature. The liquid-gas phase transition is studied as a function of the strangeness fraction. The pressure of the system cannot remain constant during the phase transition, since there are two independent conserved charges (baryon and strangeness number). In a range of temperatures around 15 MeV (precise values depending on the model used) the equation of state exhibits multiple bifurcates. The difference in the strangeness fraction f{sub s} between the liquid and gas phases is small when they coexist. The critical temperature of strange matter turns out to be a nontrivial function of the strangeness fraction.

  9. Hydration of Gas-Phase Ions Formed by Electrospray Ionization

    PubMed Central

    Rodriguez-Cruz, Sandra E.; Klassen, John S.; Williams, Evan R.

    2005-01-01

    The hydration of gas-phase ions produced by electrospray ionization was investigated. Evidence that the hydrated ions are formed by two mechanisms is presented. First, solvent condensation during the expansion inside the electrospray source clearly occurs. Second, some solvent evaporation from more extensively solvated ions or droplets is apparent. To the extent that these highly solvated ions have solution-phase structures, then the final isolated gas-phase structure of the ion will be determined by the solvent evaporation process. This process was investigated for hydrated gramicidin S in a Fourier-transform mass spectrometer. Unimolecular dissociation rate constants of isolated gramicidin S ions with between 2 and 14 associated water molecules were measured. These rate constants increased from 16 to 230 s−1 with increasing hydration, with smaller values corresponding to magic numbers. PMID:10497808

  10. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    NASA Astrophysics Data System (ADS)

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ?-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

  11. Liquid-gas phase transition of strange hadronic matter

    SciTech Connect

    P. Wang; D. B. Leinweber; A. W. Thomas; A. G. Williams

    2004-11-01

    We apply the chiral SU(3) quark mean field model to study the properties of strange hadronic matter at finite temperature. The liquid-gas phase transition is studied as a function of the strangeness fraction. The pressure of the system cannot remain constant during the phase transition, since there are two independent conserved charges (baryon and strangeness number). In a range of temperatures around 15 MeV (precise values depending on the model used) the equation of state exhibits multiple bifurcates. The difference in the strangeness fraction f{sub s} between the liquid and gas phases is small when they coexist. The critical temperature of strange matter turns out to be a non-trivial function of the strangeness fraction.

  12. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    PubMed Central

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ε-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas-phase, where they are shown to be reactive, and the solution-phase, where they are not regarded as reactive with NHS esters. PMID:25338221

  13. Gas-Phase Studies of Formamidopyrimidine Glycosylase (Fpg) Substrates.

    PubMed

    Kiruba, G S M; Xu, Jiahui; Zelikson, Victoria; Lee, Jeehiun K

    2016-03-01

    Gas-phase thermochemical properties (tautomerism, acidity, and proton affinity) have been measured and calculated for a series of nucleobase derivatives that have not heretofore been examined under vacuum. The studied species are substrates for the enzyme formamidopyrimidine glycosylase (Fpg), which cleaves damaged nucleobases from DNA. The gas-phase results are compared and contrasted to solution-phase data, to afford insight into the Fpg mechanism. Calculations are also used to probe the energetics of various possible mechanisms and to predict isotope effects that could potentially allow for discrimination between different mechanisms. Specifically, (18) O substitution at the ribose O4' is predicted to result in a normal kinetic isotope effect (KIE) for a ring-opening "endocyclic" mechanism and an inverse KIE for a direct base excision "exocyclic" pathway. PMID:26894440

  14. Star formation via the phase transition of an adiabatic gas

    NASA Technical Reports Server (NTRS)

    Tohline, Joel E.; Christodoulou, Dimitris M.

    1988-01-01

    An analytic model based on a second-order accurate global virial analysis is used to describe two stable equilibrium states for rotating gas clouds: a pressure-supported, diffuse state and a rotationally supported, compact state. Diffuse and compact equilibrium sequences are identified along which slow, secular evolution of a gas cloud can occur. A virial analysis provides analytic expressions for the limiting masses of gas clouds at points of dynamical instability. The minimum mass below which external triggers of any amplitude cannot effectively induce star formation is identified for adiabatic gas clouds. It is suggested that fluctuations in the ISM of some galaxies may actually cause star formation to proceed primarily via a phase transition, rather than via the classical Jeans instability.

  15. Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

    NASA Astrophysics Data System (ADS)

    Sullivan, R. C.; Petters, M. D.; Demott, P. J.; Kreidenweis, S. M.; Wex, H.; Niedermeier, D.; Hartmann, S.; Clauss, T.; Stratmann, F.; Reitz, P.; Schneider, J.; Sierau, B.

    2010-12-01

    During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona Test Dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed particles' heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at -30 C and -25 C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 C - intended to evaporate the sulphuric acid coating - reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability under both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

  16. Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

    NASA Astrophysics Data System (ADS)

    Sullivan, R. C.; Petters, M. D.; Demott, P. J.; Kreidenweis, S. M.; Wex, H.; Niedermeier, D.; Hartmann, S.; Clauss, T.; Stratmann, F.; Reitz, P.; Schneider, J.

    2010-07-01

    During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona test dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed aerosol's heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at -30 C and -25 C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 C - intended to evaporate the sulphuric acid coating - reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability in both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

  17. Communication: Bubbles, crystals, and laser-induced nucleation

    NASA Astrophysics Data System (ADS)

    Knott, Brandon C.; LaRue, Jerry L.; Wodtke, Alec M.; Doherty, Michael F.; Peters, Baron

    2011-05-01

    Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2 bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

  18. Preconceptual design of the gas-phase decontamination demonstration cart

    SciTech Connect

    Munday, E.B.

    1993-12-01

    Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.

  19. Gas Phase Chemical Detection with an Integrated Chemical Analysis System

    SciTech Connect

    Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent

    1999-07-08

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.

  20. Collaborative Advanced Gas Turbine Program: Phase 1. Final report

    SciTech Connect

    Hollenbacher, R.; Kesser, K.; Beishon, D.

    1994-12-01

    The Collaborative Advanced Gas Turbine (CAGT) Program is an advanced gas turbine research and development program whose goal is to accelerate the commercial availability, to within the turn of the century, of high efficiency aeroderivative gas turbines for electric power generating applications. In the first project phase, research was conducted to prove or disprove the research hypothesis that advanced aeroderivative gas turbine systems can provide a promising technology alternative, offering high efficiency and good environmental performance characteristics in modular sizes, for utility applications. This $5 million, Phase 1 research effort reflects the collaborative efforts of a broad and international coalition of industries and organizations, both public and private, that have pooled their resources to assist in this research. Included in this coalition are: electric and gas utilities, the Electric Power Research Institute, the Gas Research Institute and the principal aircraft engine manufacturers. Additionally, the US Department of Energy (DOE) and the California Energy Commission have interacted with the CAGT on both technical and executive levels as observers and sources of funding. The three aircraft engine manufacturer-led research teams participating in this research include: Rolls-Royce, Inc., and Bechtel; the Turbo Power and Marine Division of United Technologies and Fluor Daniel; and General Electric Power Generation, Stewart and Stevenson, and Bechtel. Each team has investigated advanced electric power generating systems based on their high-thrust (60,000 to 100,000 pounds) aircraft engines. The ultimate goal of the CAGT program is that the community of stakeholders in the growing market for natural-gas-fueled, electric power generation can collectively provide the right combination of market-pull and technology-push to substantially accelerate the commercialization of advanced, high efficiency aeroderivative technologies.

  1. Terahertz wave generation from gas plasma using a phase compensator with attosecond phase-control accuracy

    SciTech Connect

    Dai Jianming; Zhang, X.-C.

    2009-01-12

    We report the use of a precise phase compensator for the generation of intense terahertz waves from laser-induced gas plasma excited by a femtosecond pulse ({omega}) and its second harmonic (2{omega}) at both close contact and standoff distances. The attosecond accuracy phase-control capability of the device enables further optimization of the terahertz emission from gas plasma and elimination of the temporal walkoff between the {omega} and 2{omega} pulses traveling in dispersive media, resulting in intense terahertz generation at a distance of over 100 m by sending the optical beams far away and focusing them locally.

  2. Drag reduction in two-phase gas-liquid flows

    SciTech Connect

    Kale, D.D.

    1987-02-01

    A considerable amount of drag reduction is observed in various flow regimes for two-phase gas-liquid flow of drag reducing fluids. Various attempts have been made to correlate the amount of drag reduction, but comparison with single phase flow of drag reducing fluids has not been done in a satisfactory manner. It is well known that single phase flow of drag reducing fluids exhibits a diameter effect. In order to account for this, a plot of percent drag reduction versus friction velocity, ..mu../sup */, in the absence of a polymer additive gives a simple method of estimating the amount of drag reduction for a given flow rate and pipe diameter. For two-phase flow no such comparison has been made.

  3. Efimov-driven phase transitions of the unitary Bose gas

    NASA Astrophysics Data System (ADS)

    Krauth, Werner

    2014-05-01

    Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of unitary interactions, where Efimov trimers form, is now accessible in cold-atom experiments. We have used a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. At the end of the talk, I discuss the prospects of observing the proposed phase transitions in cold-atom systems.

  4. Efimov-driven phase transitions of the unitary Bose gas

    NASA Astrophysics Data System (ADS)

    Piatecki, Swann; Krauth, Werner

    2014-03-01

    Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of unitary interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

  5. Phase diagram of a bulk 1d lattice Coulomb gas

    NASA Astrophysics Data System (ADS)

    Démery, V.; Monsarrat, R.; Dean, D. S.; Podgornik, R.

    2016-01-01

    The exact solution, via transfer matrix, of the simple one-dimensional lattice Coulomb gas (1d LCG) model can reproduce peculiar features of ionic liquid capacitors, such as overscreening, layering, and camel- and bell-shaped capacitance curves. Using the same transfer matrix method, we now compute the bulk properties of the 1d LCG in the constant voltage ensemble. We unveil a phase diagram with rich structure exhibiting low-density disordered and high-density ordered phases, separated by a first-order phase transition at low temperature; the solid state at full packing can be ordered or not, depending on the temperature. This phase diagram, which is strikingly similar to its three-dimensional counterpart, also sheds light on the behaviour of the confined system.

  6. The influence of the gas phase chemistry of volatilised particulate phase components on gas phase budgets of radicals, NOx, and ozone

    NASA Astrophysics Data System (ADS)

    Butler, T. M.; Fountoukis, C.; Lawrence, M. G.

    2012-12-01

    Organic compounds have been shown to be a major component of atmospheric aerosol particles. A large fraction of these organic compounds are secondary in nature, being formed from primary emitted compounds through chemical reactions in the atmospheric gaseous and particulate phases. Volatile organic compounds from both anthropogenic and biogenic sources can undergo gas phase reactions which increase their level of oxidation, lowering their volatility and making them more likely to partition into the particulate phase. It is also recognised that many low- and semi- volatile compounds, which are emitted primarily in the particulate phase, can also evaporate into the gas phase, where they undergo similar oxidation chemistry. The aging of atmospheric organic aerosol includes a continuous process of evaporation, chemical reaction in the gas phase, and condensation back into the particulate phase. The identity of the molecules involved in these processes remains largely unknown; atmospheric organic aerosol is an uncharacterised mixture. Several modelling frameworks have been developed to simulate this chemical aging of atmospheric organic aerosol. These frameworks focus on simulation of characteristics such as the volatility and oxidation level of particulate phase constituents. As the nature of the organic mixture is unconstrained, a large number of possible aging schemes can account for the observed properties of atmospheric organic aerosol. This work focuses on a different aspect than the usual assessment of aerosol particle chemistry; here we instead focus on the potential impact of these aging processes on traditional ozone production chemistry, examining the extent to which this aerosol aging chemistry impacts the budgets of radicals, NOx (oxides of nitrogen, NO and NO2), and ozone. Studies are performed using a box modelling framework with a near- explicit gas phase chemical mechanism coupled to an aerosol aging framework from a state of the art chemical transport model. Several alternative aerosol aging schemes are implemented in order to gauge the sensitivity of the traditional gas phase chemistry to the inclusion of the chemistry of the volatilised organic aerosol components.

  7. Copper-catalyzed reactions: Research in the gas phase.

    PubMed

    Tsybizova, Alexandra; Roithov, Jana

    2016-01-01

    Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool for mechanistic studies in organic and organometallic chemistry. It allows investigation of reaction mixtures including monitoring of reactants, products, and intermediates, studying properties of the intermediates and their reactivity. Studying the reactive species in the gas phase can be advantageously combined with theoretical calculations. This review is focused on ESI-MS studies of copper-catalyzed reactions. Possible effects of the electrospray process on the transfer of the copper complexes to the gas phase are discussed. The plethora of mass spectrometric approaches is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples. 2015 Wiley Periodicals, Inc. Mass Spec Rev 35: 85-110, 2016. PMID:25975564

  8. Gas phase dynamics of triplet formation in benzophenone.

    PubMed

    Spighi, Gloria; Gaveau, Marc-André; Mestdagh, Jean-Michel; Poisson, Lionel; Soep, Benoît

    2014-05-28

    Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 → S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution. PMID:24728443

  9. Substituent effects on the gas-phase acidity of silane

    SciTech Connect

    Gordon, M.S.; Volk, D.E. ); Gano, D.R. )

    1989-12-20

    In a previous paper, the gas-phase acidities of XH{sub n} compounds (X = C, N, O, F, Si, P, S, Cl) were predicted with ab initio wave functions. At the MP4{sup 2} level of theory with extended basis sets acidities for these species were determined to be within 2 kcal/mol of experimental value. In the present work, with 6-31G(d) geometries and full MP4/MC-311++G{sup 6}(3df,2pd) energies, the effects of CH{sub 3}, NH{sub 2}, OH, F, SiH{sub 3}, PH{sub 2}, SH, and Cl on the gas-phase acidity of silane are examined. Only a few related calculations have been carried out. All calculations were performed with Gaussian86, and all structures were verified as minima by diagonalizing the analytically determined hessians. Only the valence electrons were correlated in the perturbation theory calculations.

  10. Gas-phase clustering of protonated amino acids with acetonitrile

    NASA Astrophysics Data System (ADS)

    Wincel, Henryk

    2010-03-01

    The gas-phase clustering reactions of protonated amino acids, AAH + (AA = Ala, Val, Ser, Phe, Pro, Gln, Lys and Arg) with acetonitrile were studied with a pulsed ion-beam high-pressure mass spectrometer. The bond energies of the AAH +(CH 3CN) complexes range from 20 to 11 kcal/mol. While for AlaH +, ValH +, SerH +, PheH +, ProH + and GlnH +, the solvation free energies decrease linearly with increasing gas-phase basicity of AA, deviations from the correlation are observed for LysH + and ArgH +. The bonding free energies for AAH +(CH 3CN) are compared with those for AAH +(H 2O) and AAH +(NH 3).

  11. Evidence of Microporous Carbon Nanosheets Showing Fast Kinetics in both Gas Phase and Liquid Phase Environments.

    PubMed

    Jin, Zhen-Yu; Xu, Yuan-Yuan; Sun, Qiang; Lu, An-Hui

    2015-10-01

    Despite the great advantages of microporous carbons for applications in gas phase separation, liquid phase enrichment, and energy storage devices, direct experiment data and theoretical calculations on the relevance of properties and structures are quite limited. Herein, two model carbon materials are designed and synthesized, i.e., microporous carbon nanosheets (MCN) and microporous carbon spheres (MCS). They both have nearly same composition, surface chemistry, and specific surface area, known morphology, but distinguishable diffusion paths. Based on these two types of materials, a reliable relationship between the morphology with different diffusion paths and adsorption kinetics in both gas phase and liquid phase environments is established. When used for CO2 capture, MCN shows a high saturated CO2 capacity of 8.52 ?mol m(-2) and 18.4 mmol cm(-3) at 273 K and ambient pressure, and its calculated first-order rate constant is ?7.4 times higher than that of MCS. Moreover, MCN shows a quick and high uptake of Cr (VI) and a higher-rate performance for supercapacitors than MCS does. These results strongly confirm that MCN exhibits improved kinetics in gas phase separation, liquid phase enrichment, and energy storage devices due to its shorter diffusion paths and larger exposed geometrical area resulting from the nanosheet structure. PMID:26192395

  12. Gas phase fractionation method using porous ceramic membrane

    DOEpatents

    Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

    1996-01-01

    Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

  13. Gas-phase terpene oxidation products: a review

    NASA Astrophysics Data System (ADS)

    Calogirou, A.; Larsen, B. R.; Kotzias, D.

    Terpenes are emitted in large quantities from vegetation into the troposphere, where they react readily with ozone, OH and NO 3 radicals leading to a number of oxidation products. The current knowledge about gas-phase terpene oxidation products is reviewed. Their formation and decomposition pathways, their products and their relevance for the troposphere, and their chemical analysis are discussed. Data on oxidation kinetics, and product yields is presented for 23 terpenes and 65 oxidation products. A total of 84 references are quoted.

  14. Gas-Phase Synthesis of Gold- and Silica-Coated Nanoparticles

    NASA Astrophysics Data System (ADS)

    Boies, Adam Meyer

    2011-12-01

    Composite nanoparticles consisting of separate core-shell materials are of interest for a variety of biomedical and industrial applications. By combining different materials at the nanoscale, particles can exhibit enhanced or multi-functional behavior such as plasmon resonance combined with superparamagnetism. Gas-phase nanoparticle synthesis processes are promising because they can continuously produce particles with high mass-yield rates. In this dissertation, new methods are investigated for producing gas-phase coatings of nanoparticles in an "assembly-line" fashion. Separate processes are developed to create coatings from silica and gold that can be used with a variety of core-particle chemistries. A photoinduced chemical vapor deposition (photo-CVD) method is used to produce silica coatings from tetraethyl orthosilicate (TEOS) on the surface of nanoparticles (diameter 5--70 nm). Tandem differential mobility analysis (TDMA) of the process demonstrates that particle coatings can be produced with controllable thicknesses (1--10 nm) by varying system parameters such as precursor flow rate. Electron microscopy and infrared spectroscopy confirm that the photo-CVD films uniformly coat the particles and that the coatings are silica. In order to describe the coating process a chemical mechanism is proposed that includes gas-phase, surface and photochemical reactions. A chemical kinetics model of the mechanism indicates that photo-CVD coating proceeds primarily through the photodecomposition of TEOS which removes ethyl groups, thus creating activated TEOS species. The activated TEOS then adsorbs onto the surface of the particle where a series of subsequent reactions remove the remaining ethyl groups to produce a silica film with an open site for further attachment. The model results show good agreement with the experimentally measured coating trends, where increased TEOS flow increases coating thickness and increased nitrogen flow decreases coating thickness. Gold decoration of nanoparticles is accomplished by evaporation of solid gold in the presence of an aerosol flow. A hot-wire generation method is developed where gold particles are produced from a composite gold-platinum wire. Investigations of the hot-wire generator show that it can produce particles with a range of sizes and that more uniform, non-agglomerated particles are produced when using smaller diameter tubes where gas velocities across the wire are higher and recirculation zones are diminished. When gold is evaporated in the presence of silica nanoparticles, the silica aerosol is decorated by gold through either homogeneous gold nucleation and subsequent scavenging by the silica nanoparticles, or by heterogeneous nucleation on the silica surface in which the gold "balls up" due to the high surface tension of gold on silica. In both cases the resulting particles exhibit a plasmon absorbance resonance typical of gold nanoparticles (lambda550 nm). Finally, the silica coating and gold decoration processes are combined with a thermal plasma technique for synthesizing iron-oxide to produce tri-layer nanoparticles.

  15. Gas-Phase Acidities of Phosphorylated Amino Acids.

    PubMed

    Stover, Michele L; Plummer, Chelsea E; Miller, Sean R; Cassady, Carolyn J; Dixon, David A

    2015-11-19

    Gas-phase acidities and heats of formation have been predicted at the G3(MP2)/SCRF-COSMO level of theory for 10 phosphorylated amino acids and their corresponding amides, including phospho-serine (pSer), -threonine (pThr), and -tyrosine (pTyr), providing the first reliable set of these values. The gas-phase acidities (GAs) of the three named phosphorylated amino acids and their amides have been determined using proton transfer reactions in a Fourier transform ion cyclotron mass spectrometer. Excellent agreement was found between the experimental and predicted GAs. The phosphate group is the deprotonation site for pSer and pThr and deprotonation from the carboxylic acid generated the lowest energy anion for pTyr. The infrared spectra were calculated for six low energy anions of pSer, pThr, and pTyr. For deprotonated pSer and pThr, good agreement is found between the experimental IRMPD spectra and the calculated spectra for our lowest energy anion structure. For pTyr, the IR spectra for a higher energy phosphate deprotonated structure is in good agreement with experiment. Additional experiments tested electrospray ionization (ESI) conditions for pTyr and determined that variations in solvent, temperature, and voltage can result in a different experimental GA value, indicating that ESI conditions affect the conformation of the pTyr anion. PMID:26492552

  16. Two-phase, gas-liquid flows in static mixers

    SciTech Connect

    Shah, N.F.; Kale, D.D. )

    1992-02-01

    This paper reports that static mixers are used for many gas-liquid two-phase operations. some of the typical applications are processing of natural gas to remove hydrogen sulfide or carbon dioxide, waste water treatment, dissolution of gases, hydrogenation, chlorination, and so on. They have experimentally studied the pressure drop for oxygen-water system in a bubble column packed with Sulzer-Koch-type mixing elements. They observed that the ratio of pressure drop through the packed bubble column to that through the unpacked one was slightly greater than one. The suitability of static mixers to mix fluids of very widely different viscosities has been demonstrated. Two-phase operations in polymer industry involve very viscous fluids. Due to the high viscosity of these fluids, the flow will be predominantly in laminar region for both fluids. There are no data on gas-liquid two-phase systems incorporating viscous Newtonian and non-Newtonian fluids where flows are predominantly in laminar region.

  17. Insights into the gas phase oxidation of Ru(0001) on the mesoscopic scale using molecular oxygen.

    PubMed

    Goritzka, Jan C; Herd, Benjamin; Krause, Philipp P T; Falta, Jens; Flege, J Ingo; Over, Herbert

    2015-06-01

    We present an extensive mesoscale study of the initial gas phase oxidation of Ru(0001), employing in situ low-energy electron microscopy (LEEM), micro low-energy electron diffraction (?-LEED) and scanning tunneling microscopy (STM). The initial oxidation was investigated in a temperature range of 500-800 K at a constant oxygen pressure of p(O2) = 4 10(-5) mbar. Depending to the preparation temperature a dramatic change of the growth morphology of the RuO2 film was observed. At lower temperature (580 K) the RuO2(110) film grows anisotropically oriented along the high symmetry directions of the Ru(0001) substrate. At higher temperature (680 K), new rotational domains of RuO2(110) begin to appear, which are slightly rotated by up to 20 with respect to the high symmetry direction. These rotated RuO2(110) domains grow along slightly rotated step edges and reveal an isotropic growth morphology. Both the growth speed and the nucleation rate differ from that of the oxide growth at lower temperature (580 K). PMID:25945505

  18. FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS AND CARBONACEOUS SOLIDS IN GAS-PHASE CONDENSATION EXPERIMENTS

    SciTech Connect

    Jaeger, C.; Huisken, F.; Henning, Th.; Mutschke, H.; Jansa, I. Llamas

    2009-05-01

    Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs) that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile three to five ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot asymptotic giant branch stars or Wolf-Rayet stars should be different and should have distinct spectral properties.

  19. Ice Nucleation in Deep Convection

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

    2001-01-01

    The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

  20. The partitioning of ketones between the gas and aqueous phases

    NASA Astrophysics Data System (ADS)

    Betterton, Eric A.

    Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H ? =0.23?? ? + 1.51; where H ? is the effective Henry's Law constant (M atm -1, and ?? ? is the Taft polar substituents constants. The results for 25C are (M atm -1) CH 3COCH 3, 32; C 6H 5COCH 3, 110; CH 2ClCOCH 3, 59; CH 3COCOCH 3, 74; CF 3COCH 3, 138. Acetophenone appears to have an abnormally high H ?. Most low molecular weight aliphatic ketones are predicted to characterized by H ??30 M atm -1 and therefore they are expected to be found in the aqueous phase at concentrations of ?5 - 0.5 ?M (given a typical gas-phase concentration range of 1-10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.

  1. ELECTRON MICROSCOPY ANALYSIS OF THE INTERMEDIATE PHASES FORMED DURING THE NUCLEATION OF YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} FILM

    SciTech Connect

    WU,L.; ZHU,Y.; SLOVYOV,V.F.; WIESMANN,H.J.; SUENAGA,M.

    2001-08-05

    Recently, considerable efforts have been made in growing bi-axially aligned thick YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) films on a flexible, textured metallic substrate for electrical power applications. The BaF{sub 2} post-deposition annealing process is one of the most promising methods. To understand the nucleation and growth mechanism of YBCO in this process, extended transmission electron microscopy analysis has been made. Here, we report on the evolution of Ba-Y oxy-fluoride which is pertinent to the epitaxial YBCO nucleation process on SrTiO{sub 3} (STO) substrate.

  2. Gas-Phase Chemical Models of Interstellar Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Lee, Ho-Hsin

    A large gas-phase chemical model of interstellar molecular clouds containing almost 4,000 gas-phase reactions involving 409 species are developed. The calculated results are in excellent agreement with observed abundances in TMC1. The effects of rapid neutral-neutral reactions in the gas phase on the synthesis of complex species is studied via a series of model calculations. Reactions between O or N atoms and carbon clusters C n are critical in hindering the synthesis of complex species. Neutral-neutral reactions involving molecular hydrogen (HAARs) are shown to aid molecular synthesis. Bistability in large gas-phase chemical networks of dense clouds is examined. The dependence of bistability on the parameter ζn H for a wide range of elemental depletions is investigated. We confirm that bistability can exist at steady-state for a range of ζn H, and the range of bistability is dependent on elemental depletions and networks utilized. The steady-state results for a variety of molecules in both the HIP and LIP solutions at a high density near 3 104 cm-3 with a standard cosmic ionization rate are also present. A model of time-dependent gas-phase chemistry in a spatially inhomogeneous cloud which is exposed on one side to an isotropic radiation field is presented. Shielding due to H2, CO and dust particles are fully considered. The cloud hydrogen number density is a function of cloud depth varying as (1-cr)-2 where r is the depth into the cloud. The cloud temperature is kept constant at 30 K. The cloud is divided into 43 slabs, which are defined so that the photodissociation rate of CO is halved as one proceeds to the next slab. Models with three different sets of initial conditions regarding hydrogen are presented here. The first model starts with atomic hydrogen in all slabs, the second starts with molecular hydrogen, and the third utilizes an H/H2 fraction with larger value in the outer slabs. The fractional abundance profiles and integrated column densities for selected species as functions of cloud depth at different times are discussed. A comparison between fractional abundances with observations in TMC1 is given. Total integrated column densities obtained via a weighting procedure are designed for unresolved distant sources.

  3. Charged supramolecular assemblies of surfactant molecules in gas phase.

    PubMed

    Bongiorno, David; Ceraulo, Leopoldo; Indelicato, Sergio; Turco Liveri, Vincenzo; Indelicato, Serena

    2016-01-01

    The aim of this review is to critically analyze recent literature on charged supramolecular assemblies formed by surfactant molecules in gas phase. Apart our specific interest on this research area, the stimuli to undertake the task arise from the widespread theoretical and applicative benefits emerging from a comprehensive view of this topic. In fact, the study of the formation, stability, and physicochemical peculiarities of non-covalent assemblies of surfactant molecules in gas phase allows to unveil interesting aspects such as the role of attractive, repulsive, and steric intermolecular interactions as driving force of supramolecular organization in absence of interactions with surrounding medium and the size and charge state dependence of aggregate structural and dynamical properties. Other interesting aspects worth to be investigated are joined to the ability of these assemblies to incorporate selected solubilizates molecules as well as to give rise to chemical reactions within a single organized structure. In particular, the incorporation of large molecules such as proteins has been of recent interest with the objective to protect their structure and functionality during the transition from solution to gas phase. Exciting fall-out of the study of gas phase surfactant aggregates includes mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in the interstellar space. Moreover, supramolecular assemblies of amphiphilic molecules in gas phase could find remarkable applications as atmospheric cleaning agents, nanosolvents and nanoreactors for specialized chemical processes in confined space. Mass spectrometry techniques have proven to be particularly suitable to generate these assemblies and to furnish useful information on their size, size polydispersity, stability, and structural organization. On the other hand molecular dynamics simulations have been very useful to rationalize many experimental findings and to furnish a vivid picture of the structural and dynamic features of these aggregates. Thus, in this review, we will focus on the most important achievements gained in recent years by both these investigative tools. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35: 170-187, 2016. PMID:26113001

  4. Experimental Studies in Ice Nucleation

    NASA Astrophysics Data System (ADS)

    Wright, Timothy Peter

    Ice nuclei play a critical role in the formation of precipitation in mixed phase clouds. Modification of IN concentrations can lead to changes in cloud lifetimes and precipitation size. Presented in this study are experimental investigations into ice nuclei in an ongoing effort to reduce the uncertainties that ice nuclei have on cloud processes and climate. This research presents a new version of the cold stage drop freezing assay to investigate the time-dependence of heterogeneous nucleation. The temperature range for the instrument spans from the melting point of water to the homogeneous freezing limit of -38 deg C. Temperature stability for the instrument allowed for experimental operation for up to four days while interrogating the same sample. Up to a one hundred fold increase in the number of analyzed drops was accomplished through an in-house written automated drop freezing detection software package. Combined instrument design improvements allow for the analysis of IN concentrations down to 10-8 ice nuclei per picoliter of sample water. A new variant of the multiple-component stochastic model for heterogeneous ice nucleation was used to investigate the time dependence of heterogeneous freezing processes. This was accomplished by analyzing how the changes in the cooling rate can impact the observed nucleation rate. The model employed four material-dependent parameters to accurately capture the observed freezing of water drops containing Arizona Test Dust. The parameters were then used to accurately predict the freezing behavior of the drops in time dependent experiments. The time dependence freezing of a wide range of materials was then investigated. These materials included the minerals montmorillonite and kaolinite, the biological proxy ice nuclei contained within the product Icemax, and flame soot generated from the incomplete combustion of ethylene gas. The time dependence for ice nuclei collected from rainwater samples was also investigated. The data show that the time dependence for all investigated materials was weak. The drop freezing assay was then employed to test the hypothesis that certain macromolecules derived from burst pollen could be efficient ice nuclei. In a new method, air samples were collected during the height of the 2013 pollen season using a particle-in-liquid impinger and the solutions were transferred to the drop freezing assay to be analyzed for ice nuclei activity. The IN concentration in collected rainwater was analyzed and compared to IN concentrations near the ground to determine if potential IN enhancement due to pollen bursting at the surface was also found within clouds. No general trend was observed between ambient pollen counts and observed IN concentrations, suggesting that ice nuclei multiplication via pollen sac rupturing and the subsequent release of macromolecules was not prevalent for the pollen types and meteorological conditions typically encountered in the Southeastern US. Additional field tests were performed in conjunction with the Wideband Integrated Bioaerosol Sensor which used UV fluorescence to determine the possible fraction of biological aerosol present at the measurement site. This instrument was operated in parallel with the particle-in-liquid impinger allowing for a comparison of ambient immersion mode ice nuclei and fluorescent particle concentrations. Two case studies provided evidence that the active release of biological ice nuclei was causally coordinated with the arrival of a cold-frontal boundary, which can loft the nuclei to seed the frontal cloud rain band.

  5. Probing solution-phase species and chemistry in the gas phase

    NASA Astrophysics Data System (ADS)

    Wang, Xue-Bin; Yang, Xin; Wang, Lai-Sheng

    Electrospray ionization not only is a powerful soft ionization technique for biological mass spectrometry but also provides an unique interface between the solution phase and the gas phase. An experimental apparatus combining electrospray with photodetachment photoelectron spectroscopy has been developed for the investigation of multiply charged anions and solution-phase species in the gas phase. In this article, the principles of this technique and our recent progress are presented and discussed. Photoelectron spectroscopy is ideal to probe free multiply charged anions and has allowed the repulsive Coulomb barrier existing universally in multiply charged anions to be directly observed and investigated. Solvation effects, solvent and counter-ion stabilization of a common inorganic doubly charged anion, SO 2- 4 , have been extensively investigated. The minimum number of water molecules needed to stabilize SO 2- 4 and its solvation behaviour have been addressed. Large hydrated SO 2- 4 clusters are found to exhibit properties of bulk aqueous solutions. We also show that the electronic structures of many inorganic metal complexes, in particular redox species, can be investigated in the gas phase using electrospray and photoelectron spectroscopy.

  6. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals.

    PubMed

    Govada, Lata; Leese, Hannah S; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S P; Chayen, Naomi E

    2016-01-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions. PMID:26843366

  7. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    NASA Astrophysics Data System (ADS)

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-02-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.

  8. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    PubMed Central

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-01-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions. PMID:26843366

  9. Homogeneous nucleation rate measurements and the properties of critical clusters

    SciTech Connect

    Wyslouzil, Barbara E.; Strey, Reinhard; Wlk, Judith; Wilemski, Gerald; Kim, Yoojeong

    2009-10-06

    By combining a range of experimental techniques, quantitative nucleation rate measurements can now be made over {approx} 20 orders of magnitude. These rates can be used to directly test the predictions of nucleation theories or scaling laws. They can also provide direct information regarding the properties of the critical clusters - the first fragments of the new phase that are in unstable equilibrium with the supersaturated mother phase. This paper reviews recent progress in the field of vapor phase nucleation with a special focus on integrating the results from supersonic nozzle and nucleation pulse chamber studies.

  10. Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation

    NASA Astrophysics Data System (ADS)

    Andr, Yamina; Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Cadiz, Fabian; Rowe, Alistair; Paget, Daniel; Petit, Elodie; Leroux, Christine; Trassoudaine, Agns; Rda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne

    2014-05-01

    High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 ?m/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 10-9 m2/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

  11. Star formation and gas phase history of the cosmic web

    NASA Astrophysics Data System (ADS)

    Snedden, Ali; Coughlin, Jared; Phillips, Lara Arielle; Mathews, Grant; Suh, In-Saeng

    2016-01-01

    We present a new method of tracking and characterizing the environment in which galaxies and their associated circumgalactic medium evolve. We have developed a structure finding algorithm that uses the rate of change of the density gradient to self-consistently parse and follow the evolution of groups/clusters, filaments and voids in large-scale structure simulations. We use this to trace the complete evolution of the baryons in the gas phase and the star formation history within each structure in our simulated volume. We vary the structure measure threshold to probe the complex inner structure of star-forming regions in poor clusters, filaments and voids. We find that the majority of star formation occurs in cold, condensed gas in filaments at intermediate redshifts (z ˜ 3). We also show that much of the star formation above a redshift z = 3 occurs in low-contrast regions of filaments, but as the density contrast increases at lower redshift, star formation switches to the high-contrast regions, or inner parts, of filaments. Since filaments bridge the void and cluster regions, it suggests that the majority of star formation occurs in galaxies in intermediate density regions prior to the accretion on to groups/clusters. We find that both filaments and poor clusters are multiphase environments distinguishing themselves by different distributions of gas phases.

  12. Gas phase oxidation downstream of a catalytic combustor

    NASA Technical Reports Server (NTRS)

    Tien, J. S.; Anderson, D. N.

    1979-01-01

    Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

  13. Eastern Gas Shales mineback report: site assessment, Phase II

    SciTech Connect

    Zielinski, R.E.; Shuck, L.Z.

    1982-09-01

    Phase I of this study provided the rationale and criteria for selecting and evaluating a site for a mineback type project. It also included the preliminary experimental results for a potential site - Sugarloaf Mountain, Rowan County, Kentucky. This document provides additional information on the site evaluation. Objectives of the current phase of the program were to extend the characterization data available on the Sugarloaf Mountain site and to provide information on the evaluation of the site's suitability as the Eastern Gas Shales Mineback Test Facility. Core geochemical analyses confirmed that the shale underlying Sugarloaf Mountain is typical of a large percentage of the shales that underlie the western portions of the Appalachian Basin. Reservoir properties were determined that provide needed data for evaluating the site and planning specific experiments. No overlying or underlying quantities of natural gas, oil, or water that would impede the safe development of the site were observed. Results of techniques and procedures employed in the evaluation of the site have application to improving current technology. Limitations of remote data acquisition were again confirmed thus further establishing the need for an Eastern Gas Shales Mineback Facility. 45 figures, 28 tables.

  14. DSMC Convergence for Microscale Gas-Phase Heat Conduction

    NASA Astrophysics Data System (ADS)

    Rader, D. J.; Gallis, M. A.; Torczynski, J. R.

    2004-11-01

    The convergence of Bird's Direct Simulation Monte Carlo (DSMC) method is investigated for gas-phase heat conduction at typical microscale conditions. A hard-sphere gas is confined between two fully accommodating walls of unequal temperature. Simulations are performed for small system and local Knudsen numbers, so continuum flow exists outside the Knudsen layers. The ratio of the DSMC thermal conductivity to the Chapman-Enskog value in the central region is determined for over 200 combinations of time step, cell size, and number of computational molecules per cell. In the limit of vanishing error, this ratio approaches 1.000 to within the correlation uncertainty. In the limit of infinite computational molecules per cell, the difference from unity depends quadratically on time step and cell size as these quantities become small. The coefficients of these quadratic terms are in good agreement with Green-Kubo values found by Hadjiconstantinou, Garcia, and co-workers. These results demonstrate that DSMC can accurately simulate microscale gas-phase heat conduction. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  15. Computational phase diagrams of noble gas hydrates under pressure

    NASA Astrophysics Data System (ADS)

    Teeratchanan, Pattanasak; Hermann, Andreas

    2015-10-01

    We present results from a first-principles study on the stability of noble gas-water compounds in the pressure range 0-100 kbar. Filled-ice structures based on the host water networks ice-Ih, ice-Ic, ice-II, and C0 interacting with guest species He, Ne, and Ar are investigated, using density functional theory (DFT) with four different exchange-correlation functionals that include dispersion effects to various degrees: the non-local density-based optPBE-van der Waals (vdW) and rPW86-vdW2 functionals, the semi-empirical D2 atom pair correction, and the semi-local PBE functional. In the He-water system, the sequence of stable phases closely matches that seen in the hydrogen hydrates, a guest species of comparable size. In the Ne-water system, we predict a novel hydrate structure based on the C0 water network to be stable or at least competitive at relatively low pressure. In the Ar-water system, as expected, no filled-ice phases are stable; however, a partially occupied Ar-C0 hydrate structure is metastable with respect to the constituents. The ability of the different DFT functionals to describe the weak host-guest interactions is analysed and compared to coupled cluster results on gas phase systems.

  16. Measurement and speciation of gas phase peroxides in the atmosphere

    SciTech Connect

    Lee, J.H.; Leahy, D.F.; Tang, I.N.; Newman, L. )

    1993-02-20

    An improved gas phase sampler and a recently developed nonenzymatic measurement method for H[sub 2]O[sub 2] and HOCH[sub 2]OOH(HMHP) are described. The gas phase sampler is equipped with a surfaceless intake to alleviate heterogeneous loss of H[sub 2]O[sub 2] in the sampling line. The nonenzymatic method makes use of the aqueous phase Fention reaction for H[sub 2]O[sub 2] measurement and is capable of speciation between H[sub 2]O[sub 2] and HMHP, using a dual channel technique. By adding a third channel employing the well-established method of p-hydroxyphenylacetic acid (POHPAA) and horseradish peroxidase for total peroxide measurement, it is possible to differentiate H[sub 2]O[sub 2], HMHP, and other organic peroxides, if present. The measurement technique was successfully deployed in a field study at George L. Smith III State Park, Georgia (82[degrees]20[prime]W, 32[degrees]30[prime]N). Preliminary data analysis indicates that the measured total peroxides range from 0.4 to [approximately]6 ppbv, depending on meteorological conditions, and that organic peroxides, mostly HMHP, constitute between 20 and 80% of the total peroxides. The work reported here represents the first continuous and real-time measurements for these peroxides in the atmosphere. 28 refs., 7 figs., 1 tab.

  17. Gas phase contributions to topochemical hydride reduction reactions

    SciTech Connect

    Kobayashi, Yoji; Li, Zhaofei; Hirai, Kei; Tassel, Cdric; Loyer, Franois; Ichikawa, Noriya; Abe, Naoyuki; Yamamoto, Takafumi; Shimakawa, Yuichi; and others

    2013-11-15

    Alkali and alkali earth hydrides have been used as solid state reductants recently to yield many interesting new oxygen-deficient transition metal oxides. These reactions have tacitly been assumed to be a solid phase reaction between the reductant and parent oxide. We have conducted a number of experiments with physical separation between the reductant and oxides, and find that in some cases reduction proceeds even when the reagents are physically separated, implying reactions with in-situ generated H{sub 2} and, to a lesser extent, getter mechanisms. Our findings change our understanding of these topochemical reactions, and should enhance the synthesis of additional new oxides and nanostructures. - Graphical abstract: Topochemical reductions with hydrides: Solid state or gas phase reaction? Display Omitted - Highlights: SrFeO{sub 2} and LaNiO{sub 2} were prepared by topochemical reduction of oxides. Separating the reducing agent (CaH{sub 2}, Mg metal) from the oxide still results in reduction. Such topochemical reactions can occur in the gas phase.

  18. Diamond nucleation using polyethene

    DOEpatents

    Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

    2013-07-23

    The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

  19. The Vacuum Bubble Nucleation

    SciTech Connect

    Lee, Bum-Hoon; Lee, Wonwoo

    2009-07-10

    We study the nucleation of a vacuum bubble via the vacuum-to-vacuum tunneling transition in curved spacetime. We consider Coleman-de Luccia's semiclassical approximation at zero temperature in pure Einstein theory of gravity and the theory with nonminimal coupling. We discuss the dynamics of a nucleated vacuum bubble.

  20. Diamond Nucleation Using Polyethene

    NASA Technical Reports Server (NTRS)

    Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

    2013-01-01

    The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

  1. Photodissociation and spectroscopy of gas phase bimetallic clusters

    SciTech Connect

    Duncan, M.A.

    1992-05-01

    Focus of the research program is the study of gas phase metal clusters for modeling fundamental interactions on metal surfaces. We characterize the chemical bonding between component atoms in clusters as well as the bonding in adsorption on cluster surfaces. Electronic spectra, vibrational frequencies and bond dissociation energies are measured for both neutral and ionized clusters with laser/mass spectrometry techniques. Small bimetallic cluster cations containing Bi/Cr, Bi/Fe, Sn/Bi, and Pb/Sb were photodissociated at various uv wavelengths. Silver dimer van der Waals complexes were produced with a series of rare gas atoms (Ar, Kr, Xe), and their vibrational frequencies and dissociation energies were obtained. (DLC)

  2. Zinc Nucleation and Growth in Microgravity

    NASA Technical Reports Server (NTRS)

    Michael, B. Patrick; Nuth, J. A., III; Lilleleht, L. U.; Vondrak, Richard R. (Technical Monitor)

    2000-01-01

    We report our experiences with zinc nucleation in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced by a heater in a vacuum chamber containing argon gas. Nucleation is induced by cooling and its onset is easily detected visually by the appearance of a cloud of solid, at least partially crystalline zinc particles. Size distribution of these particles is monitored in situ by photon correlation spectroscopy. Samples of particles are also extracted for later analysis by SEM. The initially rapid increase in particle size is followed by a slower period of growth. We apply Scaled Nucleation Theory to our data and find that the derived critical temperature of zinc, the critical cluster size at nucleation, and the surface tension values are all in reasonably good agreement with their accepted literature values.

  3. Nucleation and Crystallization in nucleated Polymers

    NASA Astrophysics Data System (ADS)

    Schick, Christoph; Zhuravlev, Evgeny; Wurm, Andreas

    2012-02-01

    Crystallization is commonly considered as nucleation followed by a growth process. Here we apply the recently developed technique, differential fast scanning calorimetry (DFSC), for a unique, new look at the crystal growth of poly(epsilon-caprolactone) (PCL) and PCL carbon nanotube composites from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity during temperature treatments by employing cooling and heating rates from 50 to 50,000 K/s. First, the crystal nucleation and overall crystallization half times were determined simultaneously in the range of temperatures where crystallization of PCL occurs. After attempting to analyze the experiments with the classical nucleation and growth model a new methodology is described, which addresses the specific problems of crystallization of flexible linear macromolecules. The structures seem to range from having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms at temperatures from the glass transition to equilibrium melting (increasingly perfect and larger crystals). The mechanisms and kinetics of growth (if any) involve a detailed understanding of the interaction with the surrounding rigid amorphous fraction (RAF) in dependence of crystal size and perfection. E. Zhuravlev, J.W.P. Schmelzer, B. Wunderlich and C. Schick, Kinetics of nucleation and crystallization in poly(epsilon-caprolactone) (PCL), Polymer 52 (2011) 1983-1997.

  4. Off-gas recycle for long-term low temperature gas phase uranium decontamination

    SciTech Connect

    Bundy, R.D.; Bunch, D.H.; Munday, E.B.; Simmons, D.W.

    1994-07-01

    In situ long-term low-temperature (LTLT) gas phase decontamination is being developed and demonstrated at the K-25 site as a technology that has the potential to substantially lower these costs while reducing criticality and safeguards concerns and worker exposure to hazardous and radioactive materials. The objective of gas phase decontamination is to employ a gaseous reagent to fluorinate nonvolatile uranium deposits to form volatile UF{sub 6}, which can be recovered by chemical trapping or freezing. The LTLT process permits the decontamination of the inside of gas-tight GDP process equipment at room temperature by substituting a long exposure to subatmospheric ClF{sub 3} for higher reaction rates at higher temperatures. Laboratory-scale experiments have demonstrated the feasibility of using LTLT gas phase decontamination with ClF{sub 3} to remove uranium deposits from this equipment. A mobile gas phase system is being designed to demonstrate the decontamination process on a full scale. If used to decontaminate the GDPs, the LTLT process would use large amounts of ClF{sub 3} and exhaust large volumes of by-product gases (ClF, C1O{sub 2}F, etc.). Initially, the excess ClF{sub 3} and reaction byproducts will be destroyed in a KOH scrubber. This paper describes a proposed system that could recover the excess ClF{sub 3}and regenerate the reaction by-products into ClF{sub 3} for use in decontamination of additional equipment. Use of this regeneration and recovery system would reduce raw material costs and also reduce the waste scrubber sludge disposal costs by reducing the amount of corrosive gases fed to the scrubber.

  5. Gas-phase synthesis of zinc oxide nanorods

    NASA Astrophysics Data System (ADS)

    Bagamadova, A. M.; Omaev, A. K.

    2015-09-01

    Gas-phase synthesis of zinc oxide (ZnO) nanorods on silicon and glass substrates has been studied. Using the proposed method, arrays of ZnO nanorods can be grown on these substrates without preliminary deposition of a thin ZnO sublayer and/or metal catalyst. The influence of the temperature regime, substrate arrangement, and growth time on the synthesis is considered. The shape, dimensions, and orientation of nanorods have been studied by electron microscopy and X-ray diffraction. Luminescence spectra and X-ray diffraction patterns of oriented arrays of nanorods have been investigated.

  6. The solar system/interstellar medium connection - Gas phase abundances

    NASA Technical Reports Server (NTRS)

    Lutz, Barry L.

    1987-01-01

    Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

  7. Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis

    PubMed Central

    Buesser, B.; Gröhn, A.J.

    2013-01-01

    Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

  8. Neurotransmitters in the Gas Phase: La-Mb Studies

    NASA Astrophysics Data System (ADS)

    Cabezas, C.; Mata, S.; Lpez, J. C.; Alonso, J. L.

    2011-06-01

    LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.

  9. Method and reactor system for rapid kill gas injection to gas phase polymerization reactors

    SciTech Connect

    Cook, J.E.; Hagerty, R.O.; Jacob, F.W.

    1987-05-19

    This patent describes a method of terminating, under emergency conditions, an olefin polymerization reaction conducted in the presence of a transition metal-based catalyst system in a substantially vertical gas phase reactor comprising a reactants inlet at the first end thereof and a venting means at the second end thereof to maintain the temperature of the reaction below the sintering temperature of the polymer. The method comprises opening the venting means and injecting an amount of a kill gas into the reaction medium in the reactor sufficient to terminate the reaction.

  10. Experimental detection of nucleation rate surface singularity

    NASA Astrophysics Data System (ADS)

    Anisimov, M. P.; Nasibulin, A. G.; Shandakov, S. D.

    2000-02-01

    As a rule, the modern theories of nucleation represent only modifications of classical theory, and they still remain unsuitable for quantitative prediction of experimental results. In order to create the universal description of supersaturated vapor nucleation, as well as evaluate other theories, we need to get the reliable experimental results. Now experimental skills are high enough for precision measurements of the vapor nucleation rates as well as for detecting and evaluating, for example, temperatures of phase transitions in the new phase critical embryos. That is, one can find experimentally the singularity of the nucleation rate surface at conditions for the critical embryo phase transitions. Visual analysis of the experimental results has the low potential to detect the nucleation rate surface singularity and the surface singularity can be missed sometimes. One major problem for singularity detection is the noise of experimental results. This problem still exists even if one has experimental results of high accuracy. The condition for surface continuity and monotony could be applied as a criterion for analysis of experimental data for the vapor nucleation rates. The criterion is tested for the broad spectrum of the experimental results in the vapor nucleation. As an example of the criterion being used, the experimental results for the n-pentanol-water binary system of nucleation have been analyzed. A peculiarity of this system is the existence of a miscibility gap between the components. It was found that the criterion as a function of n-pentanol mole fraction has the singularity in the vicinity of this gap. This singularity was smoothed in the experimental results presentation and omitted in the original research. The proposed criterion can be used to search the experimental data set singularity as a function of their variable(s).

  11. Gas-liquid phase separation in charged colloidal systems

    NASA Astrophysics Data System (ADS)

    Reščič, Jurij; Linse, Per

    2001-06-01

    A model system of charged spherical macroions and oppositely charged point counterions with a macroion-charge to counterion-charge ratio Zr=10 was investigated by employing a temperature and density scaling Monte Carlo simulation method. This approach allowed for a determination of the relative free energies among arbitrary number of thermodynamic states over a substantial region of the state space. Here, relative free energies were determined for the macroion volume fraction interval 0.04<φM<0.24 at different values of the electrostatic coupling parameter ΓII≡ZI2LB/RM, where ZI denotes the counterion charge, LB the Bjerrum length, and RM the macroion radius. The binodal curve separating the one-phase system and a gas-liquid two-phase region was determined near the critical point which was determined to φMcr=0.15 and ΓIIcr=2.6.

  12. Nucleation and stabilization of carbon-rich structures in interstellar media

    SciTech Connect

    Patra, N.; Krl, P.; Sadeghpour, H. R. E-mail: pkral@uic.edu

    2014-04-10

    We study the conditions under which carbon clusters of different sizes form and stabilize. We describe the approach to equilibrium by simulating tenuous carbon gas dynamics to long times. First, we use reactive molecular dynamics simulations to describe the nucleation of long chains, large clusters, and complex cage structures in carbon- and hydrogen-rich interstellar gas phases. We study how temperature, particle density, the presence of hydrogen, and carbon inflow affect the nucleation of molecular moieties with different characteristics, in accordance with astrophysical conditions. We extend the simulations to densities that are orders of magnitude lower than current laboratory densities, to temperatures that are relevant to circumstellar environments of planetary nebulae, and microsecond formation times. We correlate cluster size distributions from the simulations with thermodynamic equilibrium at low temperatures and gas densities, where entropy plays a significant role.

  13. Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments

    NASA Astrophysics Data System (ADS)

    He, J.; Zhang, Y.

    2013-10-01

    Gas-phase chemistry and subsequent gas-to-particle conversion processes such as new particle formation, condensation, and thermodynamic partitioning have large impacts on air quality, climate, and public health through influencing the amounts and distributions of gaseous precursors and secondary aerosols. Their roles in global air quality and climate are examined in this work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a 7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical homogenous nucleation (binary and ternary) and activation nucleation (empirical first-order power law) parameterizations, and a highly-simplified inorganic aerosol thermodynamics treatment that only simulates sulfate (SO42-) and ammonium (NH4+). In this work, a new gas-phase chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global Extension (CB05_GE) and several advanced inorganic aerosol treatments for condensation of volatile species, ion-mediated nucleation (IMN), and explicit inorganic aerosol thermodynamics have been incorporated into CESM/CAM5.1-MAM7. Comparing to the simple gas-phase chemistry, CB05_GE can predict many more gaseous species, and improve model performance for PM2.5, PM10, PM2.5 components, and some PM gaseous precursors such as SO2 and NH3 in several regions, as well as aerosol optical depth (AOD) and cloud properties (e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and shortwave cloud forcing (SWCF)) on globe. The modified condensation and aqueous-phase chemistry further improves the predictions of additional variables such as HNO3, NO2, and O3 in some regions, and new particle formation rate (J) and AOD over globe. IMN can improve the predictions of secondary PM2.5 components, PM2.5, and PM10 over Europe, as well as AOD and CDNC over globe. The explicit inorganic aerosol thermodynamics using ISORROPIA II improves the predictions of all major PM2.5 components and their gaseous precursors in some regions, as well as near-surface temperature and specific humidity, precipitation, downwelling shortwave radiation, SWCF, and cloud condensation nuclei at a supersaturation of 0.5% over globe. With all the modified and new treatments, the improved model predicts that on a global average, SWCF decreases by 2.9 W m-2, reducing the overprediction of SWCF from 7.9% to 0.9%. Uncertainties in emissions can explain largely the inaccurate predictions of precursor gases (e.g., SO2, NH3, and NO) and primary aerosols (e.g., black carbon and primary organic matter). Additional factors leading to discrepancies between model predictions and observations include uncertainties in model treatments such as dust emissions, secondary organic aerosol formation, multiple-phase chemistry, cloud microphysics, aerosol-cloud interaction, and dry and wet deposition.

  14. Demonstrating Heterogeneous Gas-Phase Catalysis with the Gas Reaction Catalyst Tube

    NASA Astrophysics Data System (ADS)

    Mattson, Bruce; Fujita, Jiro; Catahan, Rebecca; Cheng, Wes; Greimann, Jacklyn; Khandhar, Paras; Mattson, Andrew; Rajani, Anand; Sullivan, Patrick; Perkins, Ron

    2003-07-01

    Nine gas-phase reactions that can be accomplished with an inexpensive, commercially-available glass-encased, heterogeneous palladium catalyst tube are described. The catalyzed reactions are suitable for demonstrating gas-phase reactions in the classroom or teaching laboratory. The reactions described include air or oxygen oxidations (CH4 + O2, CO + O2, NH3 + O2), hydrogenation of ethene, thermal decomposition of nitrous oxide, oxidations involving nitrogen dioxide (CH4 + NO2, CO + NO2), and two oxidation reactions involving nitrous oxide (N2O + NH3, N2O + CO). Several of the reactions demonstrate processes that take place in an automotive catalytic converter. In all cases, the products can be tested by simple chemical methods.

  15. Molecular-dynamics simulations of urea nucleation from aqueous solution

    PubMed Central

    Salvalaglio, Matteo; Perego, Claudio; Giberti, Federico; Mazzotti, Marco; Parrinello, Michele

    2015-01-01

    Despite its ubiquitous character and relevance in many branches of science and engineering, nucleation from solution remains elusive. In this framework, molecular simulations represent a powerful tool to provide insight into nucleation at the molecular scale. In this work, we combine theory and molecular simulations to describe urea nucleation from aqueous solution. Taking advantage of well-tempered metadynamics, we compute the free-energy change associated to the phase transition. We find that such a free-energy profile is characterized by significant finite-size effects that can, however, be accounted for. The description of the nucleation process emerging from our analysis differs from classical nucleation theory. Nucleation of crystal-like clusters is in fact preceded by large concentration fluctuations, indicating a predominant two-step process, whereby embryonic crystal nuclei emerge from dense, disordered urea clusters. Furthermore, in the early stages of nucleation, two different polymorphs are seen to compete. PMID:25492932

  16. Crystal nucleation in Pd-Si alloys. [in containerless environment

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Turnbull, D.

    1982-01-01

    A study of the crystal phase nucleation in undercooled droplets of Pd-Si alloys with composition near the Pd(84.5)Si(15.5) eutectic composition is reported. Molten droplets are released at the top of a drop tube and solidify (to either a crystalline or glassy state) during descent. This provides a containerless (and nearly gravity free) environment so that nucleation due to container walls or vibrations is eliminated. It is found that crystallization, due to homogeneous nucleation, is bypassed in droplets of 1 mm diameter when cooled at 760 K/sec. From this an upper limit of the homogeneous nucleation rate is estimated. Results are compared with a previously published study of nucleation in 0.06 mm to 0.33 mm diameter droplets, which indicated that nucleation results from heterogeneous surface nucleation and that the number of these nuclei is dependent on the atmosphere in the drop tube.

  17. Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids

    PubMed Central

    Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

    2012-01-01

    Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO2? anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional ? or ? unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond ? electrons during NO2? rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples. PMID:21953257

  18. Ultrafast non-radiative decay of gas-phase nucleosides.

    PubMed

    De Camillis, Simone; Miles, Jordan; Alexander, Grace; Ghafur, Omair; Williams, Ian D; Townsend, Dave; Greenwood, Jason B

    2015-09-28

    The ultrafast photo-physical properties of DNA are crucial in providing a stable basis for life. Although the DNA bases efficiently absorb ultraviolet (UV) radiation, this energy can be dissipated to the surrounding environment by the rapid conversion of electronic energy to vibrational energy within about a picosecond. The intrinsic nature of this internal conversion process has previously been demonstrated through gas phase experiments on the bases, supported by theoretical calculations. De-excitation rates appear to be accelerated when individual bases are hydrogen bonded to solvent molecules or their complementary Watson-Crick pair. In this paper, the first gas-phase measurements of electronic relaxation in DNA nucleosides following UV excitation are reported. Using a pump-probe ionization scheme, the lifetimes for internal conversion to the ground state following excitation at 267 nm are found to be reduced by around a factor of two for adenosine, cytidine and thymidine compared with the isolated bases. These results are discussed in terms of a recent proposition that a charge transfer state provides an additional internal conversion pathway mediated by proton transfer through a sugar to base hydrogen bond. PMID:26299204

  19. Gas phase methylation of methyl acetoacetate. Experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Morizur, J.-P.; Martigny, I.; Taphanel, M.-H.; Tortajada, J.; Geribaldi, S.; Decouzon, M.

    1992-04-01

    Fourier transform ion cyclotron resonance and tandem mass spectrometry, complemented by semiempirical molecular orbital calculations, have been used to study gas phase methylation of methyl acetoacetate as a mixture of the keto form 1 and the enol form 2. The daughter ion spectra of the ion/molecule reaction products were compared with those of model ions generated by electron impact or chemical ionization, in order to determine the site(s) of nucleophilic reaction for the mixture. The data indicate that the site of attachment in the keto form 1 is the keto-carbonyl oxygen. For the enol form 2, no C-methylation occurs in the gas phase; the only product corresponds to O-alkylation. The results derived from D- and 13C-labelled precursors have been used to study the fragmentation mechanisms of model ions a, CH3C+ (OCH3)CH2CO2CH3; and b, CH3COCH2C+(OCH3)2. Experimental results indicate that an irreversible isomerization a --> b occurs under collisional conditions. Unimolecularly both a and b ions eliminate a neutral molecule of ketene but by different pathways. Calculations of charge distributions in 1 and 2 as well as the enthalpies of the neutral and the adduct ions are discussed.

  20. Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids

    NASA Astrophysics Data System (ADS)

    Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

    2011-09-01

    Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO{2/-} anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional ? or ? unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond ? electrons during NO{2/-} rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples.

  1. High resolution dissociative electron attachment to gas phase adenine

    SciTech Connect

    Huber, D.; Beikircher, M.; Denifl, S.; Zappa, F.; Matejcik, S.; Bacher, A.; Grill, V.; Maerk, T. D.; Scheier, P.

    2006-08-28

    The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6 eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0 to 15 eV with an electron energy resolution of about 100 meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed.

  2. Gas-phase reactivity of novel Ziegler-Natta catalysts

    SciTech Connect

    Alameddin, N.G.; Eyler, J.R.; Richardson, D.E.

    1994-12-31

    The discovery of soluble group 4 metallocene-based catalysts for the Ziegler-Natta polymerization of olefins has generated considerable interest in the field. In particular, the versatility of the Cp (cyclopentadienyl) ligand has made practical the development of a host of novel catalysts which can produce extremely regiospecific and stereospecific polymers. With further improvements in activity and stability, these catalysts are expected to make a major impact on the polymerization industry. Presently, catalyst design is driven by using the steric and electronic properties of the ligands to guide the monomer addition. However, since these ligands have considerable steric bulk, the choice of solvent will significantly affect their catalytic properties. Therefore, an understanding of the intrinsic reactivity of these catalysts independent of a solvent is one of the first steps to building a better catalyst. The work in progress is a study of the reactivity of zircononene-based catalysts in the gas phase. The authors are in the process of studying the rates of reaction of a series of these compounds with H{sub 2} as well as with a number of olefins. In the gas phase, the intrinsic reactivity of these catalysts is revealed and their chemistry can be studied in detail.

  3. CHAOS II. Gas-phase Abundances in NGC 5194

    NASA Astrophysics Data System (ADS)

    Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A.; Skillman, Evan D.; Moustakas, John

    2015-07-01

    We have observed NGC 5194 (M51a) as part of the CHemical Abundances of Spirals project. Using the Multi Object Double Spectrographs on the Large Binocular Telescope we are able to measure one or more of the temperature-sensitive auroral lines ([O iii] ?4363, [N ii] ?5755, [S iii] ?6312) and thus measure direct gas-phase abundances in 29 individual H ii regions. [O iii] ?4363 is only detected in two H ii regions, both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC 5194 and find excellent agreement ({{? }}[{log}({{O}}/{{H}})]? 0.05) for all but one region. We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC 5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter (? ? 0.08 dex), most of which can be attributed to random error and not to intrinsic dispersion. The gas-phase abundance gradient is consistent with the gradients observed in other interacting galaxies, which tend to be shallower than gradients measured in isolated galaxies. The N/O ratio (< {log}({{N}}/{{O}})> =-0.62) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10), relative to primary production mechanisms than predicted by theoretical models.

  4. Gas-phase Dissociation of homo-DNA Oligonucleotides

    NASA Astrophysics Data System (ADS)

    Stucki, Silvan R.; Dsiron, Camille; Nyakas, Adrien; Marti, Simon; Leumann, Christian J.; Schrch, Stefan

    2013-12-01

    Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS3 of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

  5. Experimental study of Gas Phase Formation and Evolution in Low fO2 Planetary Basalts.

    NASA Astrophysics Data System (ADS)

    Rutherford, M. J.; Wetzel, D. T.; Saal, A. E.; Hauri, E. H.

    2012-12-01

    The existence of a gas phase in planetary basaltic magmas is demonstrated by the ubiquitous presence of vesicles in returned lunar samples and meteorites as well as basalts from Earth and Mars. Additionally, formation of the fine-grained glass bead deposits during eruption of lunar picritic glasses required a large gas-bubble volume (> 90%) at the time of eruption/fragmentation. Up to 100-200 ppm levels of H, S, Cl and F still remain as diffusion-loss profiles in individual lunar glass beads SIMS (1), and higher volatile concentrations occur in olivine melt inclusions (2). The composition and origin of such volcanic gases were investigated by experiments on a volatile (C-O-H-S-Cl-F)-bearing picritic glass composition as a function of fO2 near iron-wustite (IW). The C-O-H species dissolved in gas-saturated basaltic melt above IW-0.5 are carbonate, OH and H2O with 100 to 10,000 ppm H2O in the sample; below IW-0.5, the C-species present (Raman and FTIR) are Fe(CO)5 (iron pentacarbonyl) and lesser CH4 [3]. The change in melt speciation in part reflects a change in calculated speciation in the coexisting gas [4]. The carbon solubility in these experimental melts increases linearly with increasing pressure; the more oxidized glasses contain 32-620 ppm C for pressures of 98 to 980 MPa, the reduced glasses contain 8-240 ppm C for pressures between 36 and 900 MPa. Thus, the C solubility of the more reduced Fe-carbonyl and CH4 is about one-half that of carbonate at the same pressure, and indicates the carrying capacity for C in reduced (i.e., lunar) magmas is much lower than it is in present day terrestrial magmas. Varioles up to 200 um in diameter formed in some experiments with higher dissolved water contents (1%); they have radiating crystalline textures (olivine, glass and poorly crystallized graphite) initiated at a central nucleation site. A sharp peak in the variole Ramen spectra indicates methane as well as CO is released during variole formation and a reaction such as 2CO = C +CO2 formed the graphite. Several series of experiments on chips of low fO2 glass created at high pressure quantify S, Cl and F partitioning into the H2O-CO gas phase with decompression steps from 200 to 40 MPa. A gas formed with the first pressure drop, indicating melt supersaturation with CO and/or CH4; H2O and lesser amounts of S, Cl and F partitioned into the initial gas, and continued to do so with additional drops in pressure. The ubiquitous Fe-metal seen in lunar picritic glasses may form by graphite oxidation, but also may form by breakdown of Fe(CO)5 as the melt continues to saturate during ascent. [1] A. E. Saal et al.(2008) Nature 454, 192-195. [2] E. H. Hauri et al (2011) Science 333, 213 -215. [3] Wetzel, D., Rutherford, M.J. Jacobsen S.D., Hauri, E.H., and Saal, A.E., (submitted); Nature Geoscience Aug. 1, 2012. [4] Zhang, C. and Duan, Z. (2009) GCA, 73, 2089-2102.

  6. ENGINE EXHAUST PARTICULATE AND GAS PHASE CONTRIBUTIONS TO VASCULAR TOXICITY

    PubMed Central

    Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

    2014-01-01

    Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicular emissions (MVE; combined gasoline and diesel exhausts) for 6 h/d × 50 days, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase 9 (MMP9) protein, 3-nitrotyrosine, and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

  7. Engine exhaust particulate and gas phase contributions to vascular toxicity.

    PubMed

    Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

    2014-05-01

    Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6 h/d × 50 d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

  8. Synthesis of Cu nanopowders by condensation from the gas phase

    NASA Astrophysics Data System (ADS)

    Chepkasov, IV; Gafner, Yu Ya; Zobov, K. V.; Batoroev, S. B.; Bardakhanov, S. P.

    2016-02-01

    In order to determine the most efficient regimes of copper nanoparticles synthesis, a series of experiments were conducted by evaporation and subsequent condensation of the raw material in an argon atmosphere. During the tests it was found that an increase of evaporation rate increases significantly the average size of the synthesized particles. However, the study of the dependence of dimensional parameters of the produced clusters on the intensity of the buffer gas flow rate has encountered significant difficulties associated because the results significantly divergent from the previously conducted experiments on the synthesis of transition metal oxides. In order to solve this contradiction the computer simulation was held of copper atoms condensation from the gas phase for the three different cooling rates and for the two final temperatures T = 373 K and T = 77 K. It was found after analysis that the rate of cooling of the gas mixture and the final temperature directly influences the number and the size of particles produced. For instance, with the 10 times of cooling rate decreases the average size of the particles obtained had increased by 2.7 times at a final temperature of 77 K and by 3.1 times at Tf = 373 K.

  9. Surfactants from the gas phase may promote cloud droplet formation.

    PubMed

    Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

    2013-02-19

    Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Khler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

  10. Nucleation Pathways of CO2 Condensation under Mesoporous Templated Glass

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Byran, Matthew S.; Warren, Garfield T.; Sokol, Paul E.; Indiana University Team; NIST Collaboration

    2015-03-01

    Carbon capture and storage (CCS) are important elements in reducing greenhouse gas emission and combating global warming. The adsorption behavior of CO2 under mesoporous confinement at room temperature is particularly relevant. , Small Angle Scattering of X-ray (SAXS) and Neutron (SANS) were used to probe the adsorption process of CO2 under such mesoporous confinement MCM-41 and details of nucleation pathways were mapped out by fitting the scattering intensities with adsorption models. From both experiments, the nucleation of CO2 on the inner pore surface of MCM-41 is found to be a two-step process; high density liquid phase CO2 first forms uniform layers following the long range translational symmetry of the porous matrix, above one CO2 filling, determined by the pore size and temperature, capillary condensation initiates. The nucleation sites formed during capillary condensation start to separate the long range symmetry from the one at uniform layers. Finally, SAXS and SANS techniques are compared and they both showed their unique properties of probing the filling-dependent structures of adsorbed CO2 under such mesoporous system.

  11. Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters

    PubMed Central

    Jurchen, John C.; Garcia, David E.; Williams, Evan R.

    2005-01-01

    Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7–19 monomer units and 2–5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation. PMID:14652186

  12. Nonstationary homogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Harstad, K. G.

    1974-01-01

    The theory of homogeneous condensation is reviewed and equations describing this process are presented. Numerical computer solutions to transient problems in nucleation (relaxation to steady state) are presented and compared to a prior computation.

  13. Musculoskeletal-induced Nucleation in Altitude Decompression Sickness

    NASA Technical Reports Server (NTRS)

    Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.

    2014-01-01

    Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.

  14. A nanoscale temperature-dependent heterogeneous nucleation theory

    SciTech Connect

    Cao, Y. Y.; Yang, G. W.

    2015-06-14

    Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale.

  15. A nanoscale temperature-dependent heterogeneous nucleation theory

    NASA Astrophysics Data System (ADS)

    Cao, Y. Y.; Yang, G. W.

    2015-06-01

    Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale.

  16. Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities

    NASA Astrophysics Data System (ADS)

    Marcolli, C.

    2014-02-01

    Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Conceptually, deposition nucleation is the only pathway that does not involve liquid water, but occurs by direct water vapor deposition onto a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact pore condensation and freezing (PCF) occurring in voids and cavities that may form between aggregated primary particles and host water at relative humidity RHw < 100% because of the inverse Kelvin effect. Homogeneous ice nucleation is expected to occur below 235 K when at least one pore is filled with water. Ice nucleation in pores may also happen in immersion mode but with a lower probability because it requires at least one active site in a water filled pore. Therefore a significant enhancement in ice nucleation efficiency is expected when temperature falls below 235 K. For a deposition nucleation process from water vapor no discontinuous change in ice nucleation efficiency should occur at T = 235 K because no liquid water is involved in this process. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T = 230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T = 210-230 K in pores with D = 2.5-3.5 nm. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters (Dp) of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with Dp = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Water adsorption isotherms of MCM-41 show that pores with Dp = 3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHi > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Given the pore structure of clay minerals, PCF should be highly efficient for T < 235 K and may occur at T > 235 K in particles that exhibit active sites for immersion freezing within pores. Most ice nucleation studies on clay minerals and mineral dusts indeed show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K in accordance with PCF and are not explicable by the classical view of deposition nucleation. PCF is probably also the prevailing ice nucleation mechanism below water saturation for glassy, soot, and volcanic ash aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition onto a solid surface.

  17. Specific, trace gas induced phase transition in copper(II)oxide for highly selective gas sensing

    NASA Astrophysics Data System (ADS)

    Kneer, J.; Wöllenstein, J.; Palzer, S.

    2014-08-01

    Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded by a dramatic drop in the overall resistivity of the CuO layer for temperatures below 200 °C. The observed percolation phenomena in this temperature regime are unique to H2S even in comparison with related volatile thio-compounds making the sensing mechanism highly selective. At elevated temperatures above 300 °C, the phase transition does not occur. This enables two distinct operational modes which are tunable via the sensor temperature and also allows for resetting the sensing layer after an electrical breakthrough.

  18. Gas-phase reactions of halogen species of atmospheric importance

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm/molecule/s. The reaction between I and NO3 was found to occur at a rate of about 60 percent of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO3 was found to be (4.5 +/- 1.9) x 10(exp -10)/cu cm/molecule/s. An upper limit for the heat of formation of IONO2 of (21 +/- 3) kJmol(exp -1) was also derived.

  19. Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed

    NASA Astrophysics Data System (ADS)

    Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

    2010-07-01

    Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

  20. Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed

    NASA Astrophysics Data System (ADS)

    Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

    2009-12-01

    Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

  1. Homogeneous nucleation of predominantly cubic ice confined in nanoporous alumina.

    PubMed

    Suzuki, Yasuhito; Duran, Hatice; Steinhart, Martin; Kappl, Michael; Butt, Hans-Jrgen; Floudas, George

    2015-03-11

    The nucleation mechanism of water can be precisely regulated by confinement within nanoporous alumina. We found a transition from heterogeneous nucleation of hexagonal ice (Ih) to homogeneous nucleation of predominantly cubic ice (Ic) with decreasing pore diameter. These results lead to a phase diagram of water under confinement. It contains a (stable) predominant Ic form, a form known to exist only in the upper atmosphere. Possible applications range from cryopreservation to construction materials like cement. PMID:25686014

  2. Phase separation in a polarized Fermi gas with spin-orbit coupling

    SciTech Connect

    Yi, W.; Guo, G.-C.

    2011-09-15

    We study the phase separation of a spin-polarized Fermi gas with spin-orbit coupling near a wide Feshbach resonance. As a result of the competition between spin-orbit coupling and population imbalance, the phase diagram for a uniform gas develops a rich structure of phase separation involving topologically nontrivial gapless superfluid states. We then demonstrate the phase separation induced by an external trapping potential and discuss the optimal parameter region for the experimental observation of the gapless superfluid phases.

  3. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

    2000-01-01

    Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

  4. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

    2000-01-01

    A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

  5. Gas-phase synthesis of magnetic metal/polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Starsich, Fabian H. L.; Hirt, Ann M.; Stark, Wendelin J.; Grass, Robert N.

    2014-12-01

    Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

  6. Silicon Nanowire-Based Devices for Gas-Phase Sensing

    PubMed Central

    Cao, Anping; Sudhölter, Ernst J.R.; de Smet, Louis C.P.M.

    2014-01-01

    Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

  7. Conformational Study of Taurine in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Cortijo, Vanessa; Sanz, M. Eugenia; Lpez, Juan C.; Alonso, Jos L.

    2009-08-01

    The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-HN between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

  8. Uv Spectroscopy on Gas Phase Cu(I)-BIPYRIDYL Complexes

    NASA Astrophysics Data System (ADS)

    Xu, Shuang; Christopher, Casey; Weber, J. Mathias

    2015-06-01

    Transition metal complexes with bipyridine ligands are of great interest in metal-organic chemistry, since they are prototypes for many applications in photochemistry and homogeneous catalysis. Under-coordinated bipyridyl complexes are elusive species in the condensed phase, and the ligand-induced changes in electronic structure are of fundamental interest. We present UV photodissociation spectra of mass-selected monocationic copper(I)-bipyridyl complexes [bpy-Cu-L]+ with different ligands (L = H2O, D2, N2, MeOH, Cl). Complexes were prepared via electrospray ionization of copper/bipyridine solutions followed by accumulation and buffer gas cooling in a cryogenic Paul trap. In addition, we show spectra of similar species based on copper oxide, [bpy-CuO-L]+.

  9. Low-energy electron collisions with gas-phase uracil.

    PubMed

    Winstead, Carl; McKoy, Vincent

    2006-11-01

    We have studied gas-phase collisions between slow electrons and uracil molecules with a view to understanding the resonance structure of the scattering cross section. Our symmetry-resolved results for elastic scattering, computed in the fixed-nuclei, static-exchange and static-exchange-plus-polarization approximations, provide locations for the expected pi* shape resonances and indicate the possible presence of a low-energy sigma* resonance as well. Electron-impact excitation calculations were carried out for low-lying triplet and singlet excitation channels and yield a very large singlet cross section. We discuss the connection between the resonances found in our elastic cross section and features observed in dissociative attachment. PMID:17100436

  10. Ceramic microreactors for heterogeneously catalysed gas-phase reactions.

    PubMed

    Knitter, Regina; Liauw, Marcel A

    2004-08-01

    The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components. PMID:15269808

  11. Optical properties of anthocyanins in the gas phase

    NASA Astrophysics Data System (ADS)

    Ge, Xiaochuan; Calzolari, Arrigo; Baroni, Stefano

    2015-01-01

    The gas-phase optical properties of the six most common anthocyanins are studied using time-dependent density-functional theory. Different anthocyanins are classified into three groups, according to the number of low-frequency peaks displayed in the UV-vis spectrum. This behavior is analyzed in terms of one-electron transitions and interaction effects, the latter being rationalized using a suitable double-pole model. Moving from PBE to hybrid exchange-correlation functionals results in a hypsochromic shift of the optical gap. While the colors thus predicted do not quite match those observed in solution, thus highlighting the importance of solvation effects, adoption of hybrid functionals remarkably determines a greater chromatic uniformity of different molecules, in qualitative agreement with experimental evidence in acidic solutions.

  12. Reduced-background gas-phase absorption spectroscopy

    SciTech Connect

    Sweetser, J.N.; Trebino, R.

    1998-08-01

    We propose and demonstrate a new method for single-shot multiplex absorption spectroscopy that permits enhanced sensitivity in the simultaneous measurement of multiple spectral lines in rapidly changing gas-phase media, such as turbulent flames. It uses an ultrashort laser pulse that propagates through the absorbing medium, for which the relevant absorption information resides in the free-induction decay that is trailing behind the transmitted pulse. Time gating out most of the transmitted pulse, but not the free-induction decay, enhances the relative fraction of light that contains absorption information when the spectrum is measured. This procedure reduces the background associated with the input light, thus enhancing detection sensitivity. {copyright} {ital 1998} {ital Optical Society of America}

  13. Structures of platinum oxide clusters in the gas phase.

    PubMed

    Kerpal, Christian; Harding, Dan J; Hermes, Alexander C; Meijer, Gerard; Mackenzie, Stuart R; Fielicke, Andr

    2013-02-14

    The structures of small gas-phase Pt(n)O(2m)(+) (n = 1-6, m = 1, 2) cluster cations have been investigated in a combined infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) study. On the basis of the infrared spectra obtained, it is concluded that in most clusters oxygen is bound dissociatively, preferring 2-fold bridge binding motifs, sometimes combined with singly coordinated terminal binding. Comparison of the oxide cluster structures with those of bare cationic platinum clusters reported previously reveals major structural changes induced in the platinum core upon oxygen binding. For some cluster sizes the presence of the Ar messenger atom(s) is found to induce a significant change in the observed cluster structure. PMID:22894744

  14. Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds

    SciTech Connect

    Nathan Robert Classen

    2002-12-31

    The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.

  15. Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase

    NASA Astrophysics Data System (ADS)

    MacLeod, N. A.; Simons, J. P.

    2007-03-01

    Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.

  16. Delayed luminescence of indole derivatives in the gas phase

    NASA Astrophysics Data System (ADS)

    Sukhodola, A. A.

    2008-07-01

    Spectral and kinetic characteristics of delayed luminescence of indole derivatives in the gas phase have been studied. The mechanism for delayed luminescence has been shown to depend on the disposition of the two lowest excited singlet ??*-states, 1La and 1Lb. For vapors of 3-methyl-and 2,3-dimethylindole having a small 1La-2Lb energy gap ?E (?E < 500 cm-1), prolonged light emissions with maxima at 525 and 540 nm, respectively, have been observed and interpreted as luminescence of free radicals formed due to dissociation of an N-H bond. For vapors of 5-methoxyindole having ?E ? 3700 cm-1, annihilation of delayed luminescence has been observed. The lifetimes for triplet states of 3-methyl-, 2,3-dimethyl-, and 5-methoxyindole at T = 373 K equal to 30, 26, and 65 sec, respectively, were calculated from the kinetics of the delayed luminescence.

  17. AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)

    EPA Science Inventory

    An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapourgas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

  18. Gas phase plasma impact on phenolic compounds in pomegranate juice.

    PubMed

    Herceg, Zoran; Kova?evi?, Danijela Bursa?; Kljusuri?, Jasenka Gajdo; Jambrak, Anet Reek; Zori?, Zoran; Dragovi?-Uzelac, Verica

    2016-01-01

    The aim of the study was to evaluate the effect of gas phase plasma on phenolic compounds in pomegranate juice. The potential of near infrared reflectance spectroscopy combined with partial least squares for monitoring the stability of phenolic compounds during plasma treatment was explored, too. Experiments are designed to investigate the effect of plasma operating conditions (treatment time 3, 5, 7 min; sample volume 3, 4, 5 cm(3); gas flow 0.75, 1, 1.25 dm(3) min(-1)) on phenolic compounds and compared to pasteurized and untreated pomegranate juice. Pasteurization and plasma treatment resulted in total phenolic content increasing by 29.55% and 33.03%, respectively. Principal component analysis and sensitivity analysis outputted the optimal treatment design with plasma that could match the pasteurized sample concerning the phenolic stability (5 min/4 cm(3)/0.75 dm(3) min(-1)). Obtained results demonstrate the potential of near infrared reflectance spectroscopy that can be successfully used to evaluate the quality of pomegranate juice upon plasma treatment considering the phenolic compounds. PMID:26213024

  19. Gas phase hydrogen permeation in alpha titanium and carbon steels

    NASA Technical Reports Server (NTRS)

    Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

    1980-01-01

    Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

  20. Estimation of gas phase mixing in packed beds

    SciTech Connect

    Frigerio, S.; Thunman, H.; Leckner, B.; Hermansson, S.

    2008-04-15

    An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

  1. Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation

    SciTech Connect

    André, Yamina Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Réda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne; Cadiz, Fabian; Rowe, Alistair; Paget, Daniel; Petit, Elodie; Leroux, Christine; Trassoudaine, Agnès

    2014-05-21

    High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 μm/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10{sup −9} m{sup 2}/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

  2. Full field gas phase velocity measurements in microgravity

    NASA Technical Reports Server (NTRS)

    Griffin, Devon W.; Yanis, William

    1995-01-01

    Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

  3. Gas phase synthesis of two ensembles of silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Mohan, A.; de Jong, M. M.; Poulios, I.; Schropp, R. E. I.; Rath, J. K.

    2015-09-01

    Dusty plasmas provide a very favorable environment for the growth of silicon nanocrystals. For application of silicon nanocrystals in a solar cell, the fabrication of monodisperse silicon quantum dots has been challenging. We report a single step method to synthesize silicon (Si) nanoparticles in a custom designed dedicated plasma reactor. The nanoparticles produced in the gas phase belong to two different phases exhibiting different structural and optical properties. Particles made in the bulk of the plasma are aggregates of crystalline particles with a mean size of 100 nm. Particles made in locally enhanced plasma regions produced at holes present in the grounded electrode contain free-standing quantum sized particles with crystallites (with mean size of 2.95 nm) embedded within an amorphous matrix. We provide insight on different plasma processes leading to the formation of aggregates and free-standing particles. We hypothesize that the free standing particles are formed due to the excess energetic electrons present in locally enhanced discharges.

  4. Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK

    NASA Astrophysics Data System (ADS)

    Tournier, Robert F.

    2014-12-01

    An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change ?p accompanying the enthalpy change -Vm?p at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T?Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

  5. Energy effects in bubble nucleation

    SciTech Connect

    Jackson, M.L. . Dept. of Chemical Engineering)

    1994-04-01

    Bubble size and number produced by desorption are important considerations for certain industrial processes such as flotation, gas stripping, and some types of chemical reactions and mass transfer. The size and number of bubbles produced by the desorption of supersaturated gases from water are shown to be a primary function of the energy available for bubble formation in a flowing system; this energy is that not dissipated in turbulence and friction. The number of nucleation sites is greatly increased when certain impurities are present, particularly surface-active agents. Low saturation pressures can produce very large numbers of very small bubbles when added energy is provided for discharge. High gas concentrations produce excess large bubbles which pass up rapidly through the much slower rising bubble mass. A combination of low saturation pressure followed by higher pressure for flow, such as by liquid pumping, results in bubble characteristics which can be controlled for applications.

  6. Assessing nucleation in cloud formation modelling for Brown Dwarf and Exoplanet atmospheres

    NASA Astrophysics Data System (ADS)

    Lee, Graham; Helling, Christiane; Giles, Helen; Bromley, Stefan

    2015-04-01

    Context. Substellar objects such as Brown Dwarfs and hot Jupiter exoplanets are cool enough that clouds can form in their atmospheres (Helling & Casewell 2014; A&ARv 22)). Unlike Earth, where cloud condensation nuclei are provided by the upward motion of sand or ash, in Brown Dwarf and hot Jupiters these condensation seeds form from the gas phase. This process proceeds in a stepwise chemical reaction of single monomer addition of a single nucleation species, referred to as homogeneous nucleation. The rate at which these seeds form is determined by the local thermodynamic conditions and the chemical composition of the local gas phase. Once the seed particles have formed, multiple materials are thermally stable and grow almost simultaneously by chemical surface reactions. This results in the growth of the condensation seeds to macroscopic particles of μm size. At the same time, the gas phase becomes depleted. Once temperatures become too high for thermal stability of the cloud particle, it evaporates until its constituents return to the gas phase. Convection from deeper atmospheric layers provides element replenishment to upper, cooler layers allowing the cloud formation process to reach a stationary state (Woitke & Helling 2003; A&A 399). Aims. The most efficient nucleation is a 'winner takes all' process as the losing molecules will condense on the surface of the faster nucleating seed particle. We apply new molecular (TiO2)N-cluster and SiO vapour data to our cloud formation model in order to re-asses the question of the primary nucleation species. Methods. We apply density functional theory (B3LYP, 6-311G(d)) using the computational chemistry package GAUSSIAN 09 to derive updated thermodynamical data for (TiO2)N-clusters as input for our TiO2 seed formation model. We test both TiO2 and SiO as primary nucleates assuming a homogeneous nucleation process and by solving a system of dust moment equations and element conservation for a pre-scribed Brown Dwarf/hot Jupiter DRIFT-PHOENIX atmospheric model temperature-pressure structure. Results. We present updated Gibbs free energies for the new (TiO2)N-clusters. We discuss the effect of this new data on the resulting cloud structure and cloud properties like particle number density, grain sizes and grain composition. We find SiO to be the more efficient nucleation species. However, subsequent SiO condensation onto seed particle mantles result in element depletion, reducing the number density of gaseous SiO and reducing the efficiency of nucleation. Therefore, TiO2 remains therefore the primary nucleation species (Lee et al. 2014; arXiv:1410.6610).

  7. Relating the hygroscopic properties of submicron aerosol to both gas- and particle-phase chemical composition in a boreal forest environment

    NASA Astrophysics Data System (ADS)

    Hong, J.; Kim, J.; Nieminen, T.; Duplissy, J.; Ehn, M.; ijl, M.; Hao, L.; Nie, W.; Sarnela, N.; Prisle, N. L.; Kulmala, M.; Virtanen, A.; Petj, T.; Kerminen, V.-M.

    2015-06-01

    Measurements of the hygroscopicity of 15-145 nm particles in a boreal forest environment were conducted using two Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) systems during the Pan-European Gas-AeroSOIs-climate interaction Study (PEGASOS) campaign in spring 2013. Measurements of the chemical composition of non-size segregated particles were also performed using a High-Resolution Aerosol Mass Spectrometer (HR-AMS) in parallel with hygroscopicity measurements. On average, the hygroscopic growth factor (HGF) of particles was observed to increase from the morning until afternoon. In case of accumulation mode particles, the main reasons for this behavior were increases in the ratio of sulfate to organic matter and oxidation level (O : C ratio) of the organic matter in the particle phase. Using an O : C dependent hygroscopic growth factor of organic matter (HGForg), fitted using the inverse Zdanovskii-Stokes-Robinson (ZSR) mixing rule, clearly improved the agreement between measured HGF and that predicted based on HR-AMS composition data. Besides organic oxidation level, the influence of inorganic species was tested when using the ZSR mixing rule to estimate the hygroscopic growth factor of organics in the aerosols. While accumulation and Aitken mode particles were predicted fairly well by the bulk aerosol composition data, the hygroscopicity of nucleation mode particles showed little correlation. However, we observed them to be more sensitive to the gas phase concentration of condensable vapors: the more there was sulfuric acid in the gas phase, the more hygroscopic the nucleation mode particles were. No clear dependence was found between the extremely low-volatility organics (ELVOCs) concentration and the HGF of particles of any size.

  8. Relating the hygroscopic properties of submicron aerosol to both gas- and particle-phase chemical composition in a boreal forest environment

    NASA Astrophysics Data System (ADS)

    Hong, J.; Kim, J.; Nieminen, T.; Duplissy, J.; Ehn, M.; Äijälä, M.; Hao, L. Q.; Nie, W.; Sarnela, N.; Prisle, N. L.; Kulmala, M.; Virtanen, A.; Petäjä, T.; Kerminen, V.-M.

    2015-10-01

    Measurements of the hygroscopicity of 15-145 nm particles in a boreal forest environment were conducted using two Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) systems during the Pan-European Gas-Aerosols-climate interaction Study (PEGASOS) campaign in spring 2013. Measurements of the chemical composition of non-size segregated particles were also performed using a high-resolution aerosol mass spectrometer (HR-AMS) in parallel with hygroscopicity measurements. On average, the hygroscopic growth factor (HGF) of particles was observed to increase from the morning until afternoon. In case of accumulation mode particles, the main reasons for this behavior were increases in the ratio of sulfate to organic matter and oxidation level (O : C ratio) of the organic matter in the particle phase. Using an O : C dependent hygroscopic growth factor of organic matter (HGForg), fitted using the inverse Zdanovskii-Stokes-Robinson (ZSR) mixing rule, clearly improved the agreement between measured HGF and that predicted based on HR-AMS composition data. Besides organic oxidation level, the influence of inorganic species was tested when using the ZSR mixing rule to estimate the hygroscopic growth factor of organics in the aerosols. While accumulation and Aitken mode particles were predicted fairly well by the bulk aerosol composition data, the hygroscopicity of nucleation mode particles showed little correlation. However, we observed them to be more sensitive to the gas phase concentration of condensable vapors: the more sulfuric acid in the gas phase, the more hygroscopic the nucleation mode particles were. No clear dependence was found between the extremely low-volatility organics concentration (ELVOC) and the HGF of particles of any size.

  9. Final Report: "Collaborative Project. Understanding the Chemical Processes That Affect Growth Rates of Freshly Nucleated Particles"

    SciTech Connect

    Smith, James N.; McMurry, Peter H.

    2015-11-12

    This final technical report describes our research activities that have, as the ultimate goal, the development of a model that explains growth rates of freshly nucleated particles. The research activities, which combine field observations with laboratory experiments, explore the relationship between concentrations of gas-phase species that contribute to growth and the rates at which those species are taken up. We also describe measurements of the chemical composition of freshly nucleated particles in a variety of locales, as well as properties (especially hygroscopicity) that influence their effects on climate. Our measurements include a self-organized, DOE-ARM funded project at the Southern Great Plains site, the New Particle Formation Study (NPFS), which took place during spring 2013. NPFS data are available to the research community on the ARM data archive, providing a unique suite observations of trace gas and aerosols that are associated with the formation and growth of atmospheric aerosol particles.

  10. Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."

    SciTech Connect

    Yu, W.; France, D. M.; Routbort, J. L.

    2011-01-19

    Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

  11. Nucleation of protein fibrillation by nanoparticles.

    PubMed

    Linse, Sara; Cabaleiro-Lago, Celia; Xue, Wei-Feng; Lynch, Iseult; Lindman, Stina; Thulin, Eva; Radford, Sheena E; Dawson, Kenneth A

    2007-05-22

    Nanoparticles present enormous surface areas and are found to enhance the rate of protein fibrillation by decreasing the lag time for nucleation. Protein fibrillation is involved in many human diseases, including Alzheimer's, Creutzfeld-Jacob disease, and dialysis-related amyloidosis. Fibril formation occurs by nucleation-dependent kinetics, wherein formation of a critical nucleus is the key rate-determining step, after which fibrillation proceeds rapidly. We show that nanoparticles (copolymer particles, cerium oxide particles, quantum dots, and carbon nanotubes) enhance the probability of appearance of a critical nucleus for nucleation of protein fibrils from human beta(2)-microglobulin. The observed shorter lag (nucleation) phase depends on the amount and nature of particle surface. There is an exchange of protein between solution and nanoparticle surface, and beta(2)-microglobulin forms multiple layers on the particle surface, providing a locally increased protein concentration promoting oligomer formation. This and the shortened lag phase suggest a mechanism involving surface-assisted nucleation that may increase the risk for toxic cluster and amyloid formation. It also opens the door to new routes for the controlled self-assembly of proteins and peptides into novel nanomaterials. PMID:17485668

  12. Gas-Phase Reactions of Halogen Species of Atmospheric Importance.

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).

  13. Measurement of Gas-phase Acids in Diesel Exhaust

    NASA Astrophysics Data System (ADS)

    Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

    2012-12-01

    Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

  14. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.

  15. Uptake of organic gas phase species by 1-methylnaphthalene.

    PubMed

    Zhang, H Z; Davidovits, P; Williams, L R; Kolb, C E; Worsnop, D R

    2005-05-01

    Organic compounds are a significant component of tropospheric aerosols. In the present study, 1-methylnaphthalene was selected as a surrogate for aromatic hydrocarbons (PAHs) found in tropospheric aerosols. Mass accommodation coefficients (alpha) on 1-methylnaphthalene were determined as a function of temperature (267 K to 298 K) for gas-phase m-xylene, ethylbenzene, butylbenzene, alpha-pinene, gamma-terpinene, p-cymene, and 2-methyl-2-hexanol. The gas uptake studies were performed with droplets maintained under liquid-vapor equilibrium conditions using a droplet train flow reactor. The mass accommodation coefficients for all of the molecules studied in these experiments exhibit negative temperature dependence. The upper and lower values of alpha at 267 and 298 K respectively are as follows: for m-xylene 0.44 +/- 0.05 and 0.26 +/- 0.03; for ethylbenzene 0.37 +/- 0.03 and 0.22 +/- 0.04; for butylbenzene 0.47 +/- 0.06 and 0.31 +/- 0.04; for alpha-pinene 0.47 +/- 0.07 and 0.10 +/- 0.05; for gamma-terpinene 0.37 +/- 0.04 and 0.12 +/- 0.06; for p-cymene 0.74 +/- 0.05 and 0.36 +/- 0.07; for 2-methyl-2-hexanol 0.44 +/- 0.06 and 0.29 +/- 0.06. The uptake measurements also yielded values for the product HD(l)(1/2) for most of the molecules studied (H = Henry's law constant, D(l) = liquid-phase diffusion coefficient). Using calculated values of D(l), the Henry's law constants (H) for these molecules were obtained as a function of temperature. The H values at 298 K in units 10(3) M atm(-1) are as follows: for m-xylene (0.48 +/- 0.05); for ethylbenzene (0.50 +/- 0.08); for butylbenzene (3.99 +/- 0.93); for alpha-pinene (0.53 +/- 0.07); for p-cymene (0.23 +/- 0.07); for 2-methyl-2-hexanol (1.85 +/- 0.29). PMID:16833713

  16. Nucleation in super-saturated products

    NASA Technical Reports Server (NTRS)

    Volmer, M.; Weber, A.

    1988-01-01

    The procedure used is based on theories of W. Gibbs. The formation of the liquid phase from a supersaturated vapor of a pure substance is first considered. A comparison is made with experience in the area of nucleation. Generally known facts and experiments are mentioned. Liquid nuclei and crystal nuclei are examined.

  17. A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced γ-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films

    SciTech Connect

    Kumar, A. K. Nanda Subramanian, B.; Prasanna, S.; Jayakumar, S.; Rao, G. Mohan

    2015-03-28

    Pure α-Al{sub 2}O{sub 3} exhibits a very high degree of thermodynamical stability among all metal oxides and forms an inert oxide scale in a range of structural alloys at high temperatures. We report that amorphous Al{sub 2}O{sub 3} thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling γ-Alumina forming almost randomly in an amorphous matrix, and with increasing frequency near the substrate/film interface. This nucleation is marked by the signature appearance of sharp (400) and (440) reflections and the formation of a diffuse diffraction halo with an outer maximal radius of ≈0.23 nm enveloping the direct beam. The microstructure then evolves by a cluster-coalescence growth mechanism suggestive of swift nucleation and sluggish diffusional kinetics, while locally the Al ions redistribute slowly from chemisorbed and tetrahedral sites to higher anion coordinated sites. Chemical state plots constructed from XPS data and simple calculations of the diffraction patterns from hypothetically distorted lattices suggest that the true origins of the diffuse diffraction halo are probably related to a complex change in the electronic structure spurred by the a-γ transformation rather than pure structural disorder. Concurrent to crystallization within the film, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source.

  18. Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate.

    PubMed

    Fukutome, Asuka; Kawamoto, Haruo; Saka, Shiro

    2015-07-01

    The gas-phase pyrolysis of levoglucosan (LG), the major intermediate species during cellulose gasification, was studied experimentally over the temperature range of 400-900?C. Gaseous LG did not produce any dehydration products, which include coke, furans, and aromatic substances, although these are characteristic products of the pyrolysis of molten LG. Alternatively, at >500?C, gaseous LG produced only fragmentation products, such as noncondensable gases and condensable C1 -C3 fragments, as intermediates during noncondensable gas formation. Therefore, it was determined that secondary reactions of gaseous LG can result in the clean (tar- and coke-free) gasification of cellulose. Cooling of the remaining LG in the gas phase caused coke formation by the transition of the LG to the molten state. The molecular mechanisms that govern the gas- and molten-phase reactions of LG are discussed in terms of the acid catalyst effect of intermolecular hydrogen bonding to promote the molten-phase dehydration reactions. PMID:26099988

  19. Homogeneous nucleation of methane hydrates: unrealistic under realistic conditions.

    PubMed

    Knott, Brandon C; Molinero, Valeria; Doherty, Michael F; Peters, Baron

    2012-12-01

    Methane hydrates are ice-like inclusion compounds with importance to the oil and natural gas industry, global climate change, and gas transportation and storage. The molecular mechanism by which these compounds form under conditions relevant to industry and nature remains mysterious. To understand the mechanism of methane hydrate nucleation from supersaturated aqueous solutions, we performed simulations at controlled and realistic supersaturation. We found that critical nuclei are extremely large and that homogeneous nucleation rates are extremely low. Our findings suggest that nucleation of methane hydrates under these realistic conditions cannot occur by a homogeneous mechanism. PMID:23148735

  20. School Heating - Gas vs. Electric. Phase 1A - Effect on Construction Costs, (Updating Phase 1 Report Dated January 1965).

    ERIC Educational Resources Information Center

    Valvoda, Frank R.

    Phase 1A updates the original study of January 1965 and contains the sevenmost recent schools which in their development stages were bid for both gas and electric heating systems. In all cases the bids were for first cost, not for ultimate operating expense. Although the differences were relatively minor, six out of the seven gas bids were lower…

  1. Gas-phase Chemistry of the Cyanate Ion, OCN-

    NASA Astrophysics Data System (ADS)

    Cole, Callie A.; Wang, Zhe-Chen; Snow, Theodore P.; Bierbaum, Veronica M.

    2015-10-01

    Cyanate (OCN-) is the only ion to date whose presence has been confirmed in the icy mantles that coat interstellar dust grains. Understanding the chemical behavior of cyanate at a fundamental level is therefore integral to the advancement of astrochemistry. We seek to unravel the chemistry of this intriguing anion through a combination of gas-phase experiments and theoretical explorations. Our approach is twofold: first, employing a flowing afterglow-selected ion flow tube apparatus, the reactions between OCN- and three of the most abundant atomic species in the interstellar medium, hydrogen, nitrogen, and oxygen, are examined. Hydrogen atoms readily react by associative detachment, but the remarkable stability of OCN- does not give rise to an observable reaction with either nitrogen or oxygen atoms. To explain these results, the potential energy surfaces of several reactions are investigated at the B3LYP/6-311++G(d,p) level of theory. Second, collision induced dissociation experiments involving deprotonated uracil, thymine, and cytosine in an ion trap mass spectrometer reveal an interesting connection between these pyrimidine nucleobase anions and OCN-. Theoretical calculations at the B3LYP/6-311++G(d,p) level of theory are performed to delineate the mechanisms of dissociation and explore the possible role of OCN- as a biomolecule precursor.

  2. Visible and ultraviolet spectroscopy of gas phase rhodamine 575 cations.

    PubMed

    Daly, Steven; Kulesza, Alexander; Knight, Geoffrey; MacAleese, Luke; Antoine, Rodolphe; Dugourd, Philippe

    2015-06-01

    The visible and ultraviolet spectroscopy of gas phase rhodamine 575 cations has been studied experimentally by action-spectroscopy in a modified linear ion trap between 220 and 590 nm and by time-dependent density functional theory (TDDFT) calculations. Three bands are observed that can be assigned to the electronic transitions S0 → S1, S0 → S3, and S0 → (S8,S9) according to the theoretical prediction. While the agreement between theory and experiment is excellent for the S3 and S8/S9 transitions, a large shift in the value of the calculated S1 transition energy is observed. A theoretical analysis of thermochromism, potential vibronic effects, and-qualitatively-electron correlation revealed it is mainly the latter that is responsible for the failure of TDDFT to accurately reproduce the S1 transition energy, and that a significant thermochromic shift is also present. Finally, we investigated the nature of the excited states by analyzing the excitations and discussed their different fragmentation behavior. We hypothesize that different contributions of local versus charge transfer excitations are responsible for 1-photon versus 2-photon fragmentation observed experimentally. PMID:25961329

  3. Gas Phase Conformations of Tetrapeptide Glycine-Phenylalanine-Glycine-Glycine

    NASA Astrophysics Data System (ADS)

    Chen, Hui-bin; Wang, Yao; Chen, Xin; Lin, Zi-jing

    2012-02-01

    Systematic search of the potential energy surface of tetrapeptide glycine-phenylalanine-glycine-glycine (GFGG) in gas phase is conducted by a combination of PM3, HF and BHandHLYP methods. The conformational search method is described in detail. The relative electronic energies, zero point vibrational energies, dipole moments, rotational constants, vertical ionization energies and the temperature dependent conformational distributions for a number of important conformers are obtained. The structural characteristics of these conformers are analyzed and it is found that the entropic effect is a dominating factor in determining the relative stabilities of the conformers. The measurements of dipole moments and some characteristic IR mode are shown to be effective approaches to verify the theoretical prediction. The structures of the low energy GFGG conformers are also analyzed in their connection with the secondary structures of proteins. Similarity between the local structures of low energy GFGG conformers and the ?-helix is discussed and many ?- and ?-turn local structures in GFGG conformers are found.

  4. Gas phase production and loss of isoprene epoxydiols.

    PubMed

    Bates, Kelvin H; Crounse, John D; St Clair, Jason M; Bennett, Nathan B; Nguyen, Tran B; Seinfeld, John H; Stoltz, Brian M; Wennberg, Paul O

    2014-02-20

    Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-β- and trans-β-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-β- and trans-β, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the δ1, cis-β, and trans-β isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions. PMID:24476509

  5. Gas-phase structures of neutral silicon clusters

    NASA Astrophysics Data System (ADS)

    Haertelt, Marko; Lyon, Jonathan T.; Claes, Pieterjan; de Haeck, Jorg; Lievens, Peter; Fielicke, Andr

    2012-02-01

    Vibrational spectra of neutral silicon clusters Sin, in the size range of n = 6-10 and for n = 15, have been measured in the gas phase by two fundamentally different IR spectroscopic methods. Silicon clusters composed of 8, 9, and 15 atoms have been studied by IR multiple photon dissociation spectroscopy of a cluster-xenon complex, while clusters containing 6, 7, 9, and 10 atoms have been studied by a tunable IR-UV two-color ionization scheme. Comparison of both methods is possible for the Si9 cluster. By using density functional theory, an identification of the experimentally observed neutral cluster structures is possible, and the effect of charge on the structure of neutrals and cations, which have been previously studied via IR multiple photon dissociation, can be investigated. Whereas the structures of small clusters are based on bipyramidal motifs, a trigonal prism as central unit is found in larger clusters. Bond weakening due to the loss of an electron leads to a major structural change between neutral and cationic Si8.

  6. Microwave spectrum and gas phase structure of maleimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Oncer, Onur; Kang, Lu; Kukolich, Stephen G.

    2016-01-01

    The rotational spectrum of maleimide was measured in the 5-12 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, all unique singly substituted 13C isotopologues, and an sbnd ND, deuterium substituted isotopologue. The parent (or normal isotopologue) rotational constants, centrifugal distortion constants, and quadrupole coupling constants are A = 6815.3251(12) MHz, B = 2361.85011(64) MHz, C = 1754.32750(64) MHz, DJ = 0.232(24) kHz, DJK = 0.546(54) kHz, 1.5?aa = 2.4227(53) MHz, and 0.25(?bb-?cc) = 1.3679(15) MHz. A best fit gas phase structure was determined using the experimental rotational constants of the isotopologues and some parameters from calculations. The inertial defect is ? = -0.054 amu 2, indicating a planar structure for maleimide, with no large amplitude motions observed on the sbnd NH hydrogen atom. Calculations using B3LYP/aug-cc-pVTZ provided rotational constants which are much closer (within 1-2%) to the experimental values compared to the MP2/aug-cc-pVTZ calculated values.

  7. Surface plasmon sensing of gas phase contaminants using optical fiber.

    SciTech Connect

    Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant

    2009-10-01

    Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.

  8. Gas-phase enantioselectivity of chiral amido[4]resorcinarene receptors.

    PubMed

    Botta, Bruno; Caporuscio, Fabiana; D'Acquarica, Ilaria; Delle Monache, Giuliano; Subissati, Deborah; Tafi, Andrea; Botta, Maurizio; Filippi, Antonello; Speranza, Maurizio

    2006-10-25

    Diastereomeric proton-bound [1(L)HA]+ complexes between selected amino acids (A=phenylglycine (Phg), tryptophan (Trp), tyrosine methyl ester (TyrOMe), threonine (Thr), and allothreonine (AThr)) and a chiral amido[4]resorcinarene receptor (1(L)) display a significant enantioselectivity when undergoing loss of the amino acid guest A by way of the enantiomers of 2-aminobutanes (B) in the gas phase. The enantioselectivity of the B-to-A displacement is ascribed to a combination of thermodynamic and kinetic factors related to the structure and the stability of the diastereomeric [1(L)HA]+ complexes and of the reaction transition states. The results of the present and previous studies allow classification of the [1(L)HA]+ complexes in three main categories wherein: i) guest A does not present any additional functionalities besides the amino acid one (alanine (Ala), Phg, and phenylalanine (Phe)); ii) guest A presents an additional alcohol function (serine (Ser), Thr, and AThr); and iii) guest A contains several additional functionalities on its aromatic ring (tyrosine (Tyr), TyrOMe, Trp, and 3,4-dihydroxyphenylalanine (DOPA)). Each category exhibits a specific enantioselectivity depending upon the predominant [1(L)HA]+ structures and the orientation of the 2-aminobutane reactant in the relevant adducts observed. The results may contribute to the understanding of the exceptional selectivity and catalytic properties of enzyme mimics towards unsolvated biomolecules. PMID:16881028

  9. Microwave spectrum and the gas phase structure of phthalimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Lin, Wei; Oncer, Onur; Kukolich, Stephen G.

    2015-11-01

    The microwave spectrum of phthalimide (PhI) was measured in the 4.8-9.5 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent and all unique single 13C substituted isotopologues. The rotational (MHz), centrifugal distortion (kHz), and quadrupole coupling constants (MHz) were determined for the parent to be A = 1745.6655(10), B = 1199.3309(6), C = 711.0864(3), DJ = 0.012(7), DJK = -0.05(9), 1.5?aa = 2.719(11), and 0.25(?bb - ?cc) = 1.236(3). Using the measured rotational constants of the isotopologues, a nonlinear least squares fit was performed to obtain the best fit gas phase structure. The inertial defect is ? = -0.175 amu 2, indicating a planar structure for PhI. Calculations using B3LYP/aug-cc-pVQZ provided rotational constants which are much closer to the experimental values compared to the MP2/6-311++G?? calculated values.

  10. Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

    NASA Astrophysics Data System (ADS)

    Lienhard, D. M.; Huisman, A. J.; Krieger, U. K.; Rudich, Y.; Marcolli, C.; Luo, B. P.; Bones, D. L.; Reid, J. P.; Lambe, A. T.; Canagaratna, M. R.; Davidovits, P.; Onasch, T. B.; Worsnop, D. R.; Steimer, S. S.; Koop, T.; Peter, T.

    2015-09-01

    New measurements of water diffusion in aerosol particles produced from secondary organic aerosol (SOA) material and from a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH4HSO4, raffinose) indicate that water diffusion coefficients are determined by several properties of the aerosol substance and cannot be inferred from the glass transition temperature or bouncing properties. Our results suggest that water diffusion in SOA particles is faster than often assumed and imposes no significant kinetic limitation on water uptake and release at temperatures above 220 K. The fast diffusion of water suggests that heterogeneous ice nucleation on a glassy core is very unlikely in these systems. At temperatures below 220 K, model simulations of SOA droplets suggest that heterogeneous ice nucleation may occur in the immersion mode on glassy cores which remain embedded in a liquid shell when experiencing fast updraft velocities. The particles absorb significant quantities of water during these updrafts which plasticize their outer layers such that these layers equilibrate readily with the gas phase humidity before the homogeneous ice nucleation threshold is reached. Glass formation is thus unlikely to restrict homogeneous ice nucleation. Only under most extreme conditions near the very high tropical tropopause may the homogeneous ice nucleation rate coefficient be reduced as a consequence of slow condensed-phase water diffusion. Since the differences between the behavior limited or non limited by diffusion are small even at the very high tropical tropopause, condensed-phase water diffusivity is unlikely to have significant consequences on the direct climatic effects of SOA particles under tropospheric conditions.

  11. Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

    NASA Astrophysics Data System (ADS)

    Lienhard, D. M.; Huisman, A. J.; Krieger, U. K.; Rudich, Y.; Marcolli, C.; Luo, B. P.; Bones, D. L.; Reid, J. P.; Lambe, A. T.; Canagaratna, M. R.; Davidovits, P.; Onasch, T. B.; Worsnop, D. R.; Steimer, S. S.; Koop, T.; Peter, T.

    2015-12-01

    New measurements of water diffusion in secondary organic aerosol (SOA) material produced by oxidation of α-pinene and in a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH4HSO4, raffinose) are presented. These indicate that water diffusion coefficients are determined by several properties of the aerosol substance and cannot be inferred from the glass transition temperature or bouncing properties. Our results suggest that water diffusion in SOA particles is faster than often assumed and imposes no significant kinetic limitation on water uptake and release at temperatures above 220 K. The fast diffusion of water suggests that heterogeneous ice nucleation on a glassy core is very unlikely in these systems. At temperatures below 220 K, model simulations of SOA particles suggest that heterogeneous ice nucleation may occur in the immersion mode on glassy cores which remain embedded in a liquid shell when experiencing fast updraft velocities. The particles absorb significant quantities of water during these updrafts which plasticize their outer layers such that these layers equilibrate readily with the gas phase humidity before the homogeneous ice nucleation threshold is reached. Glass formation is thus unlikely to restrict homogeneous ice nucleation. Only under most extreme conditions near the very high tropical tropopause may the homogeneous ice nucleation rate coefficient be reduced as a consequence of slow condensed-phase water diffusion. Since the differences between the behavior limited or non limited by diffusion are small even at the very high tropical tropopause, condensed-phase water diffusivity is unlikely to have significant consequences on the direct climatic effects of SOA particles under tropospheric conditions.

  12. Magnetic field dependence of the product yields of cycloheptanone photolysis in the dilute gas phase

    NASA Astrophysics Data System (ADS)

    Stich, E. M.; Baumeister, W. F.; Huber, J. Robert

    1984-07-01

    The product yields of the gas-phase photolysis of cycloheptanone were measured in magnetic fields up to 10 kG. The magnetic-field effect is explained in terms of the radical pair model. A reaction mechanism is proposed that explains the magnetic field dependence, pressure dependence, and excitation enegy dependence of the gas-phase photochemistry of cycloheptanone.

  13. DETERMINATION OF GAS-PHASE DIMETHYL SULFATE AND MONOMETHYL HYDROGEN SULFATE

    EPA Science Inventory

    Analytical techniques have been developed for the collection and determination of gas phase dimethyl sulfate and monomethyl sulfuric acid in the flue lines and plumes of power plants and in the ambient atmosphere. The techniques involve the collection of the gas phase species in ...

  14. DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT

    EPA Science Inventory

    The report describes-Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. his phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impur...

  15. DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT

    EPA Science Inventory

    The report describes Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. This phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impu...

  16. GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN

    EPA Science Inventory

    Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen

    Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

  17. "Cold spot" imaging with gas gangrene in three phase skeletal scintigraphy.

    PubMed

    Greene, G; Maurer, A H; Malmud, L S; Charkes, N D

    1983-09-01

    A photon deficient "cold spot" was noted in all three phases of a three phase bone study in a patient with gas gangrene of the foot. The scintigraphic findings correlated with the area of soft tissue gas noted in radiographs. PMID:6641073

  18. Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

    SciTech Connect

    Ali, A.N.; Son, S.F.; Asay, B.W.; Sander, R.K.

    2005-03-15

    Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm{+-}0.4 mm exists below which ignition by CO{sub 2} laser is not possible at the tested irradiances of 29 W/cm{sup 2} and 38 W/cm{sup 2} for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

  19. Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

    NASA Astrophysics Data System (ADS)

    Ali, A. N.; Son, S. F.; Asay, B. W.; Sander, R. K.

    2005-03-01

    Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6mm0.4mm exists below which ignition by CO2 laser is not possible at the tested irradiances of 29W /cm2 and 38W/cm2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

  20. Homogeneous crystal nucleation in binary metallic melts

    NASA Technical Reports Server (NTRS)

    Thompson, C. V.; Spaepen, F.

    1983-01-01

    A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

  1. Nonlinear Acoustical Assessment of Precipitate Nucleation

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Yost, William T.

    2004-01-01

    The purpose of the present work is to show that measurements of the acoustic nonlinearity parameter in heat treatable alloys as a function of heat treatment time can provide quantitative information about the kinetics of precipitate nucleation and growth in such alloys. Generally, information on the kinetics of phase transformations is obtained from time-sequenced electron microscopical examination and differential scanning microcalorimetry. The present nonlinear acoustical assessment of precipitation kinetics is based on the development of a multiparameter analytical model of the effects on the nonlinearity parameter of precipitate nucleation and growth in the alloy system. A nonlinear curve fit of the model equation to the experimental data is then used to extract the kinetic parameters related to the nucleation and growth of the targeted precipitate. The analytical model and curve fit is applied to the assessment of S' precipitation in aluminum alloy 2024 during artificial aging from the T4 to the T6 temper.

  2. Concurrence of aqueous and gas phase contamination of groundwater in the Wattenberg oil and gas field of northern Colorado.

    PubMed

    Li, Huishu; Son, Ji-Hee; Carlson, Kenneth H

    2016-01-01

    The potential impact of rapid development of unconventional oil and natural gas resources using hydraulic fracturing and horizontal drilling on regional groundwater quality has received significant attention. Major concerns are methane or oil/gas related hydrocarbon (such as TPHs, BTEX including benzene, toluene, ethybenzene and xylene) leaks into the aquifer due to the failure of casing and/or stray gas migration. Previously, we investigated the relationship between oil and gas activity and dissolved methane concentration in a drinking water aquifer with the major finding being the presence of thermogenic methane contamination, but did not find detectable concentrations of TPHs or BTEX. To understand if aqueous and gas phases from the producing formation were transported concurrently to drinking water aquifers without the presence of oil/gas related hydrocarbons, the ionic composition of three water groups was studied: (1) uncontaminated deep confined aquifer, (2) suspected contaminated groundwater - deep confined aquifer containing thermogenic methane, and (3) produced water from nearby oil and gas wells that would represent aqueous phase contaminants. On the basis of quantitative and spatial analysis, we identified that the "thermogenic methane contaminated" groundwater did not have similarities to produced water in terms of ionic character (e.g. Cl/TDS ratio), but rather to the "uncontaminated" groundwater. The analysis indicates that aquifer wells with demonstrated gas phase contamination have not been contacted by an aqueous phase from oil and gas operations according to the methodology we use in this study and the current groundwater quality data from COGCC. However, the research does not prove conclusively that this the case. The results may provide insight on contamination mechanisms since improperly sealed well casing may result in stray gas but not aqueous phase transport. PMID:26519629

  3. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Lass, T. J.

    1987-01-01

    A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.

  4. DNA-Assisted β-phase Nucleation and Alignment of Molecular Dipoles in PVDF Film: A Realization of Self-Poled Bioinspired Flexible Polymer Nanogenerator for Portable Electronic Devices.

    PubMed

    Tamang, Abiral; Ghosh, Sujoy Kumar; Garain, Samiran; Alam, Md Mehebub; Haeberle, Jörg; Henkel, Karsten; Schmeisser, Dieter; Mandal, Dipankar

    2015-08-01

    A flexible nanogenerator (NG) is fabricated with a poly(vinylidene fluoride) (PVDF) film, where deoxyribonucleic acid (DNA) is the agent for the electroactive β-phase nucleation. Denatured DNA is co-operating to align the molecular -CH2/-CF2 dipoles of PVDF causing piezoelectricity without electrical poling. The NG is capable of harvesting energy from a variety of easily accessible mechanical stress such as human touch, machine vibration, football juggling, and walking. The NG exhibits high piezoelectric energy conversion efficiency facilitating the instant turn-on of several green or blue light-emitting diodes. The generated energy can be used to charge capacitors providing a wide scope for the design of self-powered portable devices. PMID:26189605

  5. Measurement of soil/dust arsenic by gas phase chemiluminescence.

    PubMed

    Sawalha, Maather F; Sengupta, Mrinal K; Ohira, Shin-Ichi; Idowu, Ademola D; Gill, Thomas E; Rojo, Lila; Barnes, Melanie; Dasgupta, Purnendu K

    2008-10-19

    A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recently described for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH(3) at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reaction of AsH(3) with O(3) to produce chemiluminescence (Idowu et al., Anal. Chem. 78 (2006) 7088-7097). The same general principle has also been used in postcolumn reaction detection of As, where As species are separated chromatographically, then converted into inorganic As by passing through a UV photochemical reactor followed by AsH(3) generation and CL reaction with ozone (Idowu and Dasgupta, Anal. Chem. 79 (2007) 9197-9204). In the present paper we describe the measurement of As in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. We also compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS). As(V) was the only species found in our samples. Because of chloride interference of isobaric ArCl(+) ICP-MS analyses could only be carried out by standard addition; these results were highly correlated with direct GPCL and LC-GPCL results (r(2)=0.9935 and 1.0000, respectively). The limit of detection (LOD) in the extracts was 0.36 microg/L by direct GPCL compared to 0.1 microg/L by ICP-MS. In sulfuric acid-based extracts, the LC-GPCL method provided LODs inferior to those previously observed for water-based standards and were 2.6, 1.3, 6.7, and 6.4 microg/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), respectively. PMID:18804648

  6. IV-VI semiconductor lasers for gas phase biomarker detection

    NASA Astrophysics Data System (ADS)

    McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

    2007-09-01

    A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

  7. Gas phase selective hydrogenation over oxide supported Ni-Au.

    PubMed

    Crdenas-Lizana, Fernando; Keane, Mark A

    2015-11-14

    The chemoselective continuous gas phase (T = 573 K; P = 1 atm) hydrogenation of nitroarenes (p-chloronitrobenzene (p-CNB) and m-dinitrobenzene (m-DNB)) has been investigated over a series of oxide (Al2O3 and TiO2) supported Au and Ni-Au (1?:?10 mol ratio; 0.1-1 mol% Au) catalysts. Monometallic supported Au with mean particle size 3-9 nm promoted exclusive formation of p-chloroaniline (p-CAN) and m-nitroaniline (m-NAN). Selective hydrogenation rate was higher over smaller Au particles and can be attributed to increased surface hydrogen (from TPD measurements) at higher metal dispersion. (S)TEM analysis has confirmed an equivalent metal particle size for the supported bimetallics at the same Au loading where TPR indicates Ni-Au interaction and EDX surface mapping established Ni in close proximity to Au on isolated nanoparticles with a composition (Au/Ni) close to the bulk value (= 10). Increased spillover hydrogen due to the incorporation of Ni in the bimetallics resulted in elevated -NO2 group reduction rate. Full selectivity to p-CAN was maintained over all the bimetallic catalysts. Conversion of m-DNB over the lower loaded Ni-Au/Al2O3 generated m-NAN as sole product. An increase in Ni content (0.01 ? 0.1 mol%) or a switch from Al2O3 to TiO2 as support resulted in full -NO2 reduction (to m-phenylenediamine). Our results demonstrate the viability of Ni-promotion of Au in the continuous production of functionalised anilines. PMID:25752655

  8. Infrared spectroscopy of ionized corannulene in the gas phase

    NASA Astrophysics Data System (ADS)

    Galu, Hctor Alvaro; Rice, Corey A.; Steill, Jeffrey D.; Oomens, Jos

    2011-02-01

    The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H2, and C2Hx losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp3 hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C5v geometry induced by the Jahn-Teller effect as a consequence of the degenerate 2E1 ground electronic state. As indicated by the calculations, the five equivalent Cs minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm-1 region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

  9. Dissociative electron attachment to the gas-phase nucleobase hypoxanthine

    SciTech Connect

    Dawley, M. Michele; Tanzer, Katrin; Denifl, Stephan E-mail: Sylwia.Ptasinska.1@nd.edu; Carmichael, Ian; Ptasińska, Sylwia E-mail: Sylwia.Ptasinska.1@nd.edu

    2015-06-07

    We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C{sub 5}H{sub 4}N{sub 4}O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp − H) anion (C{sub 5}H{sub 3}N{sub 4}O{sup −}) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp − NH){sup −}, C{sub 4}H{sub 3}N{sub 4}{sup −}/C{sub 4}HN{sub 3}O{sup −}, C{sub 4}H{sub 2}N{sub 3}{sup −}, C{sub 3}NO{sup −}/HC(HCN)CN{sup −}, OCN{sup −}, CN{sup −}, and O{sup −}. Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules.

  10. Gas-Phase Combustion Synthesis of Aluminum Nitride Powder

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.

    1996-01-01

    Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.

  11. Gas-phase interactions of organotin compounds with glycine.

    PubMed

    Latrous, Latifa; Tortajada, Jeanine; Haldys, Violette; Lon, Emmanuelle; Correia, Catarina; Salpin, Jean-Yves

    2013-07-01

    Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H](+) and [(R)3Sn(Gly)](+) ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)](+) ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn](+) carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H](+) complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O?+?CO and formation of [(R)2SnOH](+) (-57?u),[(R)2SnNH2](+) (-58?u) and [(R)2SnH](+) (-73?u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O?+?CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH](+) and [(R2)SnNH2](+) ions. Interestingly, formation [(R)2SnH](+) ions is characterized by a migration of one the ? hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H](+) complexes, a preferable bidentate interaction of the type ?(2)-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn](+) ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes. PMID:23832935

  12. The Gas-Phase Deuterium Fractionation of Formaldehyde

    NASA Astrophysics Data System (ADS)

    Osamura, Yoshihiro; Roberts, Helen; Herbst, Eric

    2005-03-01

    The dominant mechanism for the deuteration of formaldehyde in the gas phase of low-temperature interstellar cloud cores occurs via reaction with the deuterating ions H2D+, HD+2, and D+3. Until now, it has been assumed that deuteration leads to an ion that, on recombination with electrons, can produce a deuterated neutral species with a statistical branching fraction. Quantum chemical calculations reported here, however, show an entirely different picture, in which the deuteration of formaldehyde leads to the molecular ion H2COD+, where the deuterium binds only on the oxygen side of the molecule. The structure is quite stable, while an alternative structure, H2DCO+, cannot be produced in a straightforward manner. Dissociative recombination of H2COD+ to reproduce a formaldehyde structure then removes the deuteration if the dissociation is direct, i.e., it occurs without change of structure. There are several possible indirect mechanisms by which dissociative recombination can lead to HDCO, however. For example, if the direct products are HCOD+H, it is possible that subsequent isomerization to HDCO can occur, although this involved process is unlikely. Another possibility is isomerization during the actual dissociation of the H2COD intermediate. Models of deuterium fractionation in which dissociative recombination is predominantly direct are presented, and it is found that the deuterium fractionation of formaldehyde to form both HDCO and D2CO can still occur via other mechanisms, although with less efficiency than previously obtained. If the dissociative recombination is half indirect, however, then we can recover the previously calculated efficiency.

  13. Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.

    2001-01-01

    Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

  14. Capillary effects on gas hydrate three-phase stability in marine sediments

    NASA Astrophysics Data System (ADS)

    Liu, X.; Flemings, P. B.

    2013-12-01

    We study the three-phase (Liquid + Gas + Hydrate) stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases. The aqueous CH4 solubilities required for forming hydrate (L+H) and free gas (L+G) in different pore sizes can be met in a three-phase zone. The top of the three-phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases. The thickness of the three-phase zone increases as the pore size distribution widens. The top of the three-phase zone can either overlie the three-phase stability depth at deepwater Blake Ridge or underlie the three-phase stability depth at Hydrate Ridge in shallow water. Our model prediction is compatible with worldwide observations that the bottom-simulating reflector is systematically shifted upward relative to the bulk equilibrium depth as water depth (pressure) is increased. The gas hydrate and free gas saturations of the three-phase zone at Blake Ridge Comparison of the globally compiled BSR temperatures with the three-phase equilibrium curves for the systems of pure CH4 + 3.5 wt.% seawater (solid line) and pure CH4 + 2.0 wt.% seawater (dotted line). The discrepancies between the observed BSR temperature and the calculated three-phase temperature are systematically larger in deep water than in shallow water.

  15. CO2 Capture from Flue Gas by Phase Transitional Absorption

    SciTech Connect

    Liang Hu

    2009-06-30

    A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.

  16. Homogeneous nucleation rate measurements in supersaturated water vapor.

    PubMed

    Brus, David; Zdmal, Vladimr; Smolk, Jir

    2008-11-01

    The rate of homogeneous nucleation in supersaturated vapors of water was studied experimentally using a thermal diffusion cloud chamber. Helium was used as a carrier gas. Our study covers a range of nucleation rates from 3x10(-1) to 3x10(2) cm(-3) s(-1) at four isotherms: 290, 300, 310, and 320 K. The molecular content of critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of nucleation rate of water on saturation ratio were compared with the prediction of the classical theory of homogeneous nucleation, the empirical prediction of Wolk et al. [J. Chem. Phys. 117, 10 (2002)], the scaled model of Hale [Phys. Rev. A 33, 4156 (1986)], and the former nucleation onset data. PMID:19045352

  17. Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities

    NASA Astrophysics Data System (ADS)

    Marcolli, C.

    2013-06-01

    Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Water in pores can freeze in immersion mode at T > 235 K if the pore walls contain an active site. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with T = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Many clay minerals and mineral dusts show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K. Such an increase is difficult to explain when ice nucleation is supposed to occur by a deposition mechanism, but evident when assuming freezing in pores, because for homogeneous ice nucleation only small pore volumes are needed, while heterogeneous ice nucleation requires larger pore structures to contain at least one active site for immersion nucleation. Together, these pieces of evidence strongly suggest that ice nucleation within pores should be the prevailing freezing mechanism of clay minerals for RHw below water saturation. Extending the analysis to other types of ice nuclei shows that freezing in pores and cracks is probably the prevailing ice nucleation mechanism for glassy and volcanic ash aerosols at RHw below water saturation. Freezing of water in carbon nanotubes might be of significance for ice nucleation by soot aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition on a solid surface. Inspection of ice nuclei with a close lattice match to ice, such as silver iodide or SnomaxTM, show that for high ice nucleation efficiency below water saturation the presence of impurities or cracks on the surface may be essential. Soluble impurities promote the formation of a liquid phase below water saturation in patches on the surface or as a complete surface layer that offers an environment for immersion freezing. If porous aerosol particles come in contact with semivolatile vapors, these will condense preferentially in pores before a coating on the surface of the particles is formed. A pore partially filled with condensed species attracts water at lower RHw than an empty pore, but the aqueous solution that forms in the pore will freeze at a higher RHi than pure water. The ice nucleation ability of pores completely filled with condensed organic species might be totally impeded. Pores might also be important for preactivation, the capability of a particle to nucleate ice at lower RHi in subsequent experiments when compared to the first initial ice nucleation event. Preactivation has often been explained by persistence of ice embryos at specific sites like dislocations, steps, kinks or pores. However, it is not clear how such features can preserve an ice embryo at RHi < 100%. Rather, ice embryos could be preserved when embedded in water. To keep liquid water at RHw well below 100%, narrow pores are needed but to avoid a strong melting point depression large pores are favorable. A narrow pore opening and a large inner volume are combined in "ink bottle" pores. Such "ink bottle" pores would be suited to preserve ice at RHi < 100% and can arise e.g. in spaces between aggregated particles.

  18. Nucleation of gold nanoparticle superclusters from solution.

    PubMed

    Yan, H; Cingarapu, S; Klabunde, K J; Chakrabarti, A; Sorensen, C M

    2009-03-01

    Measurements of the solubility curve of a quasi-monodisperse gold nanoparticle solution are given. Temperature quenches from the one-phase to the two-phase regime yielded superclusters of the nanoparticle solid phase with sizes that depended on the quench depth. Classical nucleation theory was used to describe these sizes using a value of the surface tension for the nanoparticle solid phase of 0.042 erg/cm2. This value is consistent with molecule size scaling of the surface tension. In total these results show that suspensions of nanoparticles act like molecular solutions. PMID:19392530

  19. Three-phase measurements of oil and gas trapping in sand packs

    NASA Astrophysics Data System (ADS)

    Al Mansoori, Saleh K.; Iglauer, Stefan; Pentland, Christopher H.; Blunt, Martin J.

    2009-10-01

    We measure the trapped saturations of oil and gas as a function of initial saturation in water-wet sand packs. We start with a water-saturated column and inject octane (oil), while water and oil are produced from the bottom. Once water production has ceased, air (gas) then enters from the top, allowing oil and gas to drain under gravity for different times. Finally water is then injected from the bottom to trap both oil and gas. The columns are sliced and the fluids analyzed using gas chromatography. We find that for high initial gas saturations more gas can be trapped in the presence of oil than in a two-phase (gas/water) system. The residual gas saturation can be over 20% compared to 14% in two-phase flow [Al Mansoori SK, Iglauer S, Pentland CH, Bijeljic B, Blunt MJ. Measurements of non-wetting phase trapping applied to carbon dioxide storage. Energy Procedia 2009;1(1):3173-80]. This is unlike previous measurements on consolidated media, where the trapped gas saturation is either similar or lower to that reached in an equivalent two-phase experiment. For lower initial gas saturation, the amount of trapping follows the initial-residual trend seen in two-phase experiments. The amount of oil trapped is insensitive to initial gas saturation or the amount of gas that is trapped, again in contrast to measurements on consolidated media. More oil is trapped than would be predicted from an equivalent two-phase (oil/water) system, although the trapped saturation is never larger than the maximum reached in two-phase flow (around 11%) [Pentland CH, Al Mansoori SK, Iglauer S, Bijeljic B, Blunt MJ. Measurement of non-wetting phase trapping in sand packs. In: SPE 115697, proceedings of the SPE annual technical conference and exhibition, Denver, Colorado, USA; 21-24 September 2008]. These initially surprising results are explained in the context of oil layer stability and the competition between snap-off and piston-like advance. In two-phase systems, displacement is principally by cooperative piston-like advance with relatively little trapping, whereas in consolidated media snap-off is generally more significant. However, oil layer collapse events during three-phase waterflooding rapidly trap the oil which acts as a barrier to direct water/gas displacement, except by snap-off, leading to enhanced gas trapping.

  20. Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process

    NASA Technical Reports Server (NTRS)

    Nikolaev, Pavel

    2004-01-01

    The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

  1. A new method for measurement of gas-phase ammonia and amines in air

    NASA Astrophysics Data System (ADS)

    Dawson, M. L.; Gomez, A.; Arquero, K. D.; Perraud, V. M.; Finlayson-Pitts, B. J.

    2013-12-01

    Accurately predicting particle formation and growth from gas phase precursors is an essential component of modeling the impact of particulate matter on human health, visibility and climate. While the reactions of ammonia with nitric and sulfuric acids to form particulate nitrate and sulfate particles is well known, it has been recently recognized that gas-phase amines, even at low ppb levels, significantly enhance particle formation from common atmospheric acids. As a result, accurate data on the sources, sinks and typical background concentrations of gas-phase amines, are crucial to predicting new particle formation in the atmosphere. However, gas-phase amines are notoriously difficult to measure, as they have a tendency to stick to surfaces, including sampling lines and inlets. In addition, background amine concentrations in the atmosphere are typically a few ppb or lower, requiring low detection limits for ambient sampling techniques. Here we report the development of a simple, reliable method for detection of gas-phase amines at atmospherically relevant concentrations using collection on a cation exchange sorbent followed by in-line extraction and ion chromatography. Gas-phase standards of several amines and ammonia are used to characterize the technique and results from ambient samples in an agricultural area are presented. The application of this technique to field measurements as well as to laboratory measurements of new particle formation from gas-phase ammonia and amines are discussed.

  2. Bleb Nucleation through Membrane Peeling

    NASA Astrophysics Data System (ADS)

    Alert, Ricard; Casademunt, Jaume

    2016-02-01

    We study the nucleation of blebs, i.e., protrusions arising from a local detachment of the membrane from the cortex of a cell. Based on a simple model of elastic linkers with force-dependent kinetics, we show that bleb nucleation is governed by membrane peeling. By this mechanism, the growth or shrinkage of a detached membrane patch is completely determined by the linker kinetics, regardless of the energetic cost of the detachment. We predict the critical nucleation radius for membrane peeling and the corresponding effective energy barrier. These may be typically smaller than those predicted by classical nucleation theory, implying a much faster nucleation. We also perform simulations of a continuum stochastic model of membrane-cortex adhesion to obtain the statistics of bleb nucleation times as a function of the stress on the membrane. The determinant role of membrane peeling changes our understanding of bleb nucleation and opens new directions in the study of blebs.

  3. Bleb Nucleation through Membrane Peeling.

    PubMed

    Alert, Ricard; Casademunt, Jaume

    2016-02-12

    We study the nucleation of blebs, i.e., protrusions arising from a local detachment of the membrane from the cortex of a cell. Based on a simple model of elastic linkers with force-dependent kinetics, we show that bleb nucleation is governed by membrane peeling. By this mechanism, the growth or shrinkage of a detached membrane patch is completely determined by the linker kinetics, regardless of the energetic cost of the detachment. We predict the critical nucleation radius for membrane peeling and the corresponding effective energy barrier. These may be typically smaller than those predicted by classical nucleation theory, implying a much faster nucleation. We also perform simulations of a continuum stochastic model of membrane-cortex adhesion to obtain the statistics of bleb nucleation times as a function of the stress on the membrane. The determinant role of membrane peeling changes our understanding of bleb nucleation and opens new directions in the study of blebs. PMID:26919015

  4. Carrier Gas Dependent Evaporation Energy of GaN Estimated from Spiral Growth Rates in Selective-Area Metalorganic Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Akasaka, Tetsuya; Kobayashi, Yasuyuki; Kasu, Makoto; Yamamoto, Hideki

    2013-10-01

    GaN was grown in spiral growth mode by metalorganic vapor phase epitaxy in selective areas having screw-type dislocations. Relationships between the growth rate and supersaturation provide a novel way to estimate the evaporation energy of GaN, which turns out to be carrier gas dependent: 4.30.9 eV for N2 and 2.10.4 eV for H2. The latter is significantly smaller, probably due to enhanced etching by H2. Suppression of excessive nucleation by etching in H2 may be responsible for the formation of step-free GaN surfaces at low temperatures in selective areas free from screw-type dislocations.

  5. Nucleation in Synoptically Forced Cirrostratus

    NASA Technical Reports Server (NTRS)

    Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

    2004-01-01

    Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

  6. Gas phase chemistry of bis(pentamethylcyclopentadienyl)samarium

    SciTech Connect

    Marcalo, J.; Matos, A.P. de; Evans, W.

    1996-01-09

    The gas phase chemistry of bis(pentamethylcyclopentadienyl)samarium, (C{sub 5}Me{sub 5}){sub 2}Sm, was studied by Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS). Positive electron impact (EI) spectra showed the formation of (C{sub 5}Me{sub 5}){sub 2} Sm{sup +}, (C{sub 5}Me{sub 5})Sm{sup +}, and Sm{sup +}. All three ions reacted with (C{sub 5}Me{sub 5}){sub 2}Sm by charge transfer, as verified by double-resonance techniques, and (C{sub 5}Me{sub 5})Sm{sup +} also formed the (C{sub 5}Me{sub 5}){sub 3}Sm{sub 2}{sup +} ion in a condensation reaction with neutral (C{sub 5}Me{sub 5}){sub 2}Sm. The laser desorption/ionization (LDI) spectra showed, in addition to (C{sub 5}Me{sub 5}){sub 2}Sm{sup +}, (C{sub 5}Me{sub 5})Sm{sup +}, and Sm{sup +}, the formation of (C{sub 5}Me{sub 4}H)Sm{sup +} and (C{sub 5}Me{sub 4}CH{sub 2})Sm{sup +}. The latter species most probably involves a tetramethylfulvenide ligand. Access to all of the ionic species cited here could also be obtained by reacting laser-desorbed Sm{sup +} ions with pentamethylcyclopentadiene, C{sub 5}Me{sub 5}H. (C{sub 5}Me{sub 4}CH{sub 2})Sm{sup +}, (C{sub 5}Me{sub 4}H)Sm{sup +}, and (C{sub 5}Me{sub 5})Sm{sup +} were formed as primary products, and the metallocene ion (C{sub 5}Me{sub 5}){sub 2}Sm{sup +} resulted from the rapid addition of C{sub 5}Me{sub 5}H to (C{sub 5}Me{sub 4}CH{sub 2})Sm{sup +}. 34 refs., 4 figs.

  7. Gas-phase lithium cation affinity of glycine.

    PubMed

    Bourcier, Sophie; Chiaa, Ru Xuan; Mimbong, Rosa Ngo Biboum; Bouchoux, Guy

    2015-01-01

    The gas-phase lithium cation binding thermochemistry of glycine has been determined theoretically by quantum chemical calculations at the G4 level and experimentally by the extended kinetic method using electrospray ionization quadrupole time-of-flight tandem mass spectrometry. The lithium cation affinity of glycine, ?(Li)H(298)(GLY), i.e. the?(Li)H(298) of the reaction GlyLi(+)? Gly + Li(+)) given by the G4 method is equal to 241.4 kJ.mol(-1) if only the most stable conformer of glycine is considered or to 242.3 kJ.mol(-1) if the 298K equilibrium mixture of neutral conformers is included in the calculation. The ?(Li)H(298)(GLY) deduced from the extended kinetic method is obviously dependent on the choice of the Li(+) affinity scale, thus?(Li)H(298)(GLY) is equal to 228.70.9(2.0) kJ.mol(- 1) if anchored to the recently re-evaluated lithium cation affinity scale but shifted to 235.41.0 kJ.mol(-1) if G4 computed lithium cation affinities of the reference molecules is used. This difference of 6.3 kJ.mol(-1) may originate from a compression of the experimental lithium affinity scale in the high ?(Li)H(298) region. The entropy change associated with the reaction GlyLi(+)?Gly + Li(+) reveals a gain of approximately 15 J.mol(-) 1.K(-1) with respect to monodentate Li(+) acceptors. The origin of this excess entropy is attributed to the bidentate interaction between the Li(+) cation and both the carbonyl oxygen and the nitrogen atoms of glycine. The computed G4 Gibbs free energy,?(Li)G(298)(GLY) is equal to 205.3 kJ.mol(-1), a similar result, 201.03.4 kJ.mol(-1), is obtained from the experiment if the?(Li)G(298) of the reference molecules is anchored on the G4 results. PMID:26307695

  8. Gas-phase spectroscopy of a vinylheptafulvene chromophore.

    PubMed

    Elm, Jonas; Stockett, Mark; Houmøller, Jørgen; Åxman Petersen, Michael; Mikkelsen, Kurt V; Brøndsted Nielsen, Mogens; Brøndsted Nielsen, Steen

    2015-01-01

    The intrinsic spectral properties of the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch, free of solvent interactions, were investigated both experimentally and theoretically. A quaternary ammonium group was incorporated via an ethylene bridge to allow for the transfer of charged molecules to the gas phase by electrospray ionization, leaving the chromophore part itself neutral. Absorption by the two isomers was identified from ion dissociation (i.e., action spectroscopy) using a home-built sector instrument. Several fragment ions were observed, and dissociation occurred both at the charge tag side chain and at the chromophore unit itself. We measured an absorption band of VHF with a maximum at 430 ± 20 nm (2.9 eV ± 0.1 eV) but no band was discernible for the DHA in the visible region. This shows that little interconversion between the two isomers occurs during the electrospray and the subsequent trapping in an octopole for 25 ms; the latter is needed to produce ion bunches for spectroscopy where a pulsed laser system is used. For comparison, density functional theoretical calculations predicted lowest-energy vertical excitations of 3.33 eV to 3.48 eV for the DHA and 3.02 eV to 3.08 eV for the VHF (the ranges are based on the use of different functionals), which correspond to a maximal deviation between theory and experiment of 0.1 eV in the case of the VHF. The absorption by the bare ions is significantly blue-shifted compared to that by VHF in acetonitrile solution (2.64 eV), but similar within the experimental uncertainty to that by VHF in cyclohexane (2.78 eV); the transition, therefore has a significant charge-transfer character. Finally, we find that the absorption of two photons is needed to cause fragmentation of the VHF on the microsecond time scale, which indicates that prompt fragmentation from the electronically excited state or prior to the intramolecular vibrational redistribution of the excess energy plays no role. This is of particular importance for the use of the photosystem in advanced materials or molecular electronics where high photostability is required to allow for numerous isomerization cycles. PMID:26307736

  9. Detection methods for atoms and radicals in the gas phase

    NASA Astrophysics Data System (ADS)

    Hack, W.

    This report lists atoms and free radicals in the gas phase which are of interest for environmental and flame chemistry and have been detected directly. The detection methods which have been used are discussed with respect to their range of application, specificity and sensitivity. In table 1, detection methods for the five atoms of group IV (C, Si, Ge, Sn, Pb) and about 60 radicals containing at least one atom of group IV are summarized (CH, Cd, Cf, CC1, CBr, Cn, Cs, CSe, CH2, CD2, Chf, Cdf, CHC1, CHBr, CF2, CC12, CBr2, CFC1, CFBr, CH3, CD3, CF3, CH2F, CH2C1, CH2Br, CHF2, CHC12, CHBr2, Hco, Fco, CH30, CD30, CH2OH, CH3S, Nco, CH4N, CH302, CF302; C2, C2N, C2H, C20, C2HO, C2H3, C2F3, C2H5, C2HsO, C2H4OH, CH3CO, CD3CO, C2H3O, C2H502, CH3COO2, C2H4N, C2H6N, C3; Si, SiF, SiF2, SiO, SiC, Si2; Ge, GeC, GeO, GeF, GeF2, GeCl2, Sn, SnF, SnO, SnF2, Pb, PbF, PbF2, PbO, PbS). In table 2 detection methods for about 25 other atoms and 60 radicals are listed: (H, D, O, O2, Oh, Od, HO2, DO2, F, Ci, Br, I, Fo, Cio, BrO, Io, FO2, C1O2, Li, Na, K, Rb, Cs, N, N3, Nh, Nd, Nf, Nci, NBr, NH2, ND2, Nhd, Nhf, NF2, NC12, N2H3, No, NO2, NO3, Hno, Dno, P, Ph, Pd, Pf, Pci, PH2, PD2, PF2, Po, As, AsO, AsS, Sb, Bi, S, S2, Sh, Sd, Sf, SF2, So, Hso, Dso, Sn, Se, Te, Se2, SeH, SeD, SeF, SeO, SeS, SeN, TeH, TeO, Bh, BH2, Bo, Bn, B02, Cd, Hg, UF5). The tables also cite some recent kinetic applications of the various methods.

  10. The gas-phase thermal chemistry of tetralin and related model systems

    SciTech Connect

    Malandra, J.

    1993-05-01

    The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.

  11. Application of gamma densitometry and statistical signal analysis to gas phase velocity measurements in pipeline hydrotransport

    NASA Astrophysics Data System (ADS)

    Zych, Marcin; Hanus, Robert; Petryka, Leszek; ?wisulski, Dariusz; Strz?powicz, Anna; Zych, Piotr

    2015-05-01

    The work presents selected methods of signal analysis used in the processing of data obtained from radiometric probes. The used data came from an exemplary study of a two-phase liquid-gas flow at the laboratory installation. In such rigs many possible transport types may be observed, i.e. slug, plug and bubble flow, and each of them gives different signal-to-noise ratio of recorded data. Therefore, available radiometric methods of gas phase velocity measurements give diverse accuracies. Authors consider several improvements of data acquisition and processing which increase possibility of the flow type recognition and higher accuracy of the gas phase velocity estimation.

  12. Gas phase dispersion in compost as a function of different water contents and air flow rates

    NASA Astrophysics Data System (ADS)

    Sharma, Prabhakar; Poulsen, Tjalfe G.

    2009-07-01

    Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.

  13. Gas phase dispersion in compost as a function of different water contents and air flow rates.

    PubMed

    Sharma, Prabhakar; Poulsen, Tjalfe G

    2009-07-21

    Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity. PMID:19419792

  14. Substrate orientation effects on the nucleation and growth of the M{sub n+1}AX{sub n} phase Ti{sub 2}AlC

    SciTech Connect

    Tucker, Mark D.; Guenette, Mathew C.; Bilek, Marcela M. M.; McKenzie, David R.; Persson, Per O. A.; Rosen, Johanna

    2011-01-01

    The M{sub n+1}AX{sub n} (MAX) phases are ternary compounds comprising alternating layers of a transition metal carbide or nitride and a third ''A-group'' element. The effect of substrate orientation on the growth of Ti{sub 2}AlC MAX phase films was investigated by studying pulsed cathodic arc deposited samples grown on sapphire cut along the (0001), (1010), and (1102) crystallographic planes. Characterization of these samples was by x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. On the (1010) substrate, tilted (1018) growth of Ti{sub 2}AlC was found, such that the TiC octahedra of the MAX phase structure have the same orientation as a spontaneously formed epitaxial TiC sublayer, preserving the typical TiC-Ti{sub 2}AlC epitaxial relationship and confirming the importance of this relationship in determining MAX phase film orientation. An additional component of Ti{sub 2}AlC with tilted fiber texture was observed in this sample; tilted fiber texture, or axiotaxy, has not previously been seen in MAX phase films.

  15. Volumes of critical bubbles from the nucleation theorem

    NASA Astrophysics Data System (ADS)

    Wilemski, Gerald

    2006-09-01

    A corollary of the nucleation theorem due to Kashchiev [Nucleation: Basic Theory with Applications (Butterworth-Heinemann, Oxford, 2000)] allows the volume V* of a critical bubble to be determined from nucleation rate measurements. The original derivation was limited to one-component, ideal gas bubbles with a vapor density much smaller than that of the ambient liquid. Here, an exact result is found for multicomponent, nonideal gas bubbles. Provided a weak density inequality holds, this result reduces to Kashchiev's simple form which thus has a much broader range of applicability than originally expected. Limited applications to droplets are also mentioned, and the utility of the pT,x form of the nucleation theorem as a sum rule is noted.

  16. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.

    1992-01-01

    Modifications to the nucleation apparatus suggested by our first microgravity flight campaign are complete. These included a complete 'repackaging' of the equipment into three racks along with an improved vapor spout shutter mechanism and additional thermocouples for gas temperature measurements. The 'repackaged' apparatus was used in two KC-135 campaigns: one during the week of June 3, 1991 consisting of two flights with Mg and two with Zn, and another series consisting of three flights with Zn during the week of September 23, 1991. Our effort then was focused on the analysis of these data, including further development of the mathematical models to generate the values of temperature and supersaturation at the observed points of nucleation. The efforts to apply Hale's Scaled Nucleation Theory to our experimental data have met with only limited success, most likely due to still inadequate temperature field determination. Work on the development of a preliminary particle collector system designed to capture particles from the region of nucleation and condensation, as well as from other parts of the chamber, are discussed.

  17. An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above

    NASA Technical Reports Server (NTRS)

    Disimile, Peter J.; Heist, Timothy J.

    1990-01-01

    The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.

  18. Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers

    SciTech Connect

    Schauer, J.J.; Cass, G.R.

    2000-05-01

    Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contribution to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbon and particle-phase organic compounds as tracers to determine source contributions to non-methane organic gases in the atmosphere. Both models are applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes. Source contributions to fine particle air quality are calculated for two urban sites, Fresno and Bakersfield, and one background site, Kern Wildlife Refuge. Primary particle emissions from hardwood combustion, softwood combustion, diesel engines, meat cooking, and gasoline-powered motor vehicles contribute on average 79% of the airborne fine particle organic compound mass at the urban sites during both episodes with smaller but still measurable contributions from fine particle road dust and natural gas combustion aerosol. Anthropogenic primary particle sources contribute less than 10% of the fine particle mass concentration at the background site. The combined gas-phase and particle-phase organic compound receptor model shows that gasoline-powered motor vehicle exhaust and gasoline vapors are the largest contributors to nonmethane organic gases concentrations followed by natural gas leakage. Smaller but statistically significant contributions to organic vapors from wood combustion, meat cooking, and diesel exhaust also are quantified.

  19. Two-stage coal liquefaction without gas-phase hydrogen

    DOEpatents

    Stephens, H.P.

    1986-06-05

    A process is provided for the production of a hydrogen-donor solvent useful in the liquefaction of coal, wherein the water-gas shift reaction is used to produce hydrogen while simultaneously hydrogenating a donor solvent. A process for the liquefaction of coal using said solvent is also provided. The process enables avoiding the use of a separate water-gas shift reactor as well as high pressure equipment for liquefaction. 3 tabs.

  20. On the Ice Nucleation Spectrum

    NASA Technical Reports Server (NTRS)

    Barahona, D.

    2012-01-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

  1. Experimental study on natural circulation precooling of cryogenic pump system with gas phase inlet reflux configuration

    NASA Astrophysics Data System (ADS)

    Chen, G. B.; Zhong, Y. K.; Zheng, X. L.; Li, Q. F.; Xie, X. M.; Gan, Z. H.; Huang, Y. H.; Tang, K.; Kong, B.; Qiu, L. M.

    2003-12-01

    A novel gas-phase inlet configuration in the natural circulation system instead of the liquid-phase inlet is introduced to cool down a cryogenic pump system from room temperature to cryogenic temperatures, effectively. The experimental apparatus is illustrated and test process is described. Heat transfer and pressure drop data during the cool-down process are recorded and portrayed. By contrast with liquid-phase inlet configuration, experimental results demonstrate that the natural circulation with the gas-phase inlet configuration is an easier and more controllable way to cool down the pump system and maintain it at cryogenic temperatures.

  2. Development of Numerical Simulation Method for Compressible Gas-Liquid Two-Phase Flows

    NASA Astrophysics Data System (ADS)

    Tamura, Y.

    2015-12-01

    A numerical simulation method of compressible gas-liquid two-phase flow is developed for analyses of a cavitation bubble. Thermodynamic state of both phases is described with stiffened gas equation of state. Interface of two phases is captured by Level-Set method. As internal energy jump between two phases is critical for the stability of computation, total energy equation is modified so that inviscid flux of energy is smoothly connected across the interface. Detail of governing equations as well as their discretization is described followed by the result of one-dimensional simple example computation.

  3. Crystallization and nucleation kinetics in volcanic systems

    NASA Astrophysics Data System (ADS)

    Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

    2011-12-01

    The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orlans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

  4. Direct nucleation of crystalline SiGe on substrates by reactive thermal CVD with Si{sub 2}H{sub 6} and GeF{sub 4}

    SciTech Connect

    Yoshizawa, Fumio; Shiota, Kunihiro; Inoue, Daisuke; Hanna, Junichi

    1997-07-01

    Polycrystalline SiGe (poly-SiGe) film growth by reactive thermal CVD with a gaseous mixture of Si{sub 2}H{sub 6} and GeF{sub 4} was investigated on various substrates such as Al, Cr, Pt, Si, ITO, ZnO and thermally grown SiO{sub 2}. In Ge-rich film growth, SEM observation in the early stage of the film growth revealed that direct nucleation of crystallites took place on the substrates. The nucleation was governed by two different mechanisms: one was a heterogeneous nucleation on the surface and the other was a homogeneous nucleation in the gas phase. In the former case, the selective nucleation was observed at temperatures lower than 400 C on metal substrates and Si, where the activation of adsorbed GeF{sub 4} on the surface played a major role for the nuclei formation, leading to the selective film growth. On the other hand, the direct nucleation did not always take place in Si-rich film growth irrespective of the substrates and depended on the growth rate. In a growth rate of 3.6nm/min, the high crystallinity of poly-Si{sub 0.95}Ge{sub 0.05} in a 220nm-thick film was achieved at 450 C due to the no initial deposition of amorphous tissue on SiO{sub 2} substrates.

  5. NAT nucleation and denitrification in the polar stratosphere

    NASA Astrophysics Data System (ADS)

    Groo, Jens-Uwe; Engel, Ines; Hoyle, Christopher R.; Luo, Beiping; Peter, Thomas; Frey, Wiebke; Molleker, Sergej; Borrmann, Stephan; Schlager, Hans; Vmel, Holger; Kivi, Rigel; Walker, Kaley A.; Santee, Michelle L.; Stiller, Gabriele; Pitts, Michael; Mller, Rolf

    2013-04-01

    Nitric acid trihydrate (NAT) particles in the polar stratosphere are known to influence the chemistry of ozone depletion. NAT particles, along with other liquid and crystalline particles, provide heterogeneous surfaces for chlorine activation. More importantly, they can take up significant amounts of HNO3 from the gas phase and transport HNO3 downward by sedimentation. This can lead to denitrification, in the Arctic typically at altitudes above about 20 km, and a re-nitrification below, at the level where the NAT particles evaporate. The nucleation rate of NAT particles is a critical parameter for the simulation of this process. Very low NAT nucleation rates around 2?10-9cm-3s-1 have been deduced for low NAT supersaturations from observations. In previous studies, vertical HNO3 transport has been successfully simulated by Lagrangian 3-D simulations using a constant NAT nucleation rate of around 2?10-9cm-3s-1, for the Arctic winters in the years 2003 and 2005. However, for winter 2009/2010, this approach does not generate satisfying results. Here, saturation dependent NAT nucleation rates were derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), observations under the assumption that NAT nucleates heterogeneously on dust particles that are characterized by active sites with a certain occurrence probability distribution depending on the contact angle. Simulations with the Zurich Optical and Microphysical box Model (ZOMM) along back-trajectories starting from points where PSCs were observed by CALIPSO allow the parametrisation of heterogeneous nucleation rates for NAT and ice on dust, and the reproduction of the different PSC classes observed. We present simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS) of the winter 2009/2010 applying this new parametrisation of heterogeneous NAT nucleation rates. The CLaMS simulation is initialized using a combination of MLS, MIPAS-ENVISAT and ACE-FTS data. The simulation shows good agreement of chemical trace species with observations, especially H2O and HNO3, which are important for the reliable simulation of HNO3 supersaturations over NAT. This is shown by comparisons with in-situ CFH frost point hygrometer sondes and satellite based observations of H2O and HNO3 by MIPAS-ENVISAT, MLS, and ACE-FTS. Comparisons of the size distribution of the simulated NAT particles with the observations by a Forward Scattering Spectrometer Probe (FSSP) aboard the high-flying research aircraft Geophysica operated in the winter 2009/2010 indicate good agreement, even though the largest observed particles are not reproduced by the simulation. The simulation also reproduces the HNO3 redistribution in the Arctic winter 2009/2010 with denitrification and the re-nitrification peaks as observed by the ACE-FTS satellite instrument and in-situ observations by the SIOUX instrument operated aboard Geophysica.

  6. Interface roughening and defect nucleation during solid phase epitaxy regrowth of doped and intrinsic Si{sub 0.83}Ge{sub 0.17} alloys

    SciTech Connect

    D'Angelo, D.; Piro, A. M.; Terrasi, A.; Grimaldi, M. G.; Mirabella, S.; Bongiorno, C.

    2007-05-15

    Metastable pseudomorphic Si{sub 0.83}Ge{sub 0.17} with thickness of 135 nm was deposited on (001) Si substrate by molecular beam epitaxy and amorphized to a depth of {approx}360 nm, using 3x10{sup 15} cm{sup -2} Ge ions at 270 keV. Samples were regrown by solid phase epitaxy in the 500-600 degree sign C temperature range. The regrowth rate was measured in situ by time resolved reflectivity, while the structure of the epilayers was investigated by transmission electron microscopy. Three regions can be distinguished in SiGe after solid phase epitaxy, independent of the annealing temperature: (1) a 20 nm defect-free layer close to the original crystal-amorphous interface, (2) a middle region with a high density of planar defects, and (3) a layer with dislocations and stacking faults extending up to the surface. The activation energy of the SiGe solid phase epitaxy is equal to the activation energy of Si except in the middle region. The amorphous-crystal interface evolution was studied by transmission electron microscopy of partially regrown samples. In order to study the effects of dopants, some samples were also implanted with B{sup +} and Sb{sup +} ions. At the ion projected range (125 nm for both implants) the regrowth rate increases by a factor of 3 with respect to the unimplanted SiGe, but the defect-free layer again is found to be about 20 nm in all cases. Moreover, the activation energy of the solid phase epitaxy regrowth process does not depend on dopant introduction, while the only observable effect of B or Sb incorporation is a smoothness of the amorphous-crystal interface during solid phase epitaxy.

  7. FACTORS INFLUENCING THE DEPOSITION OF A COMPOUND THAT PARTITIONS BETWEEN GAS AND PARTICULATE PHASES

    EPA Science Inventory

    How will atmospheric deposition behave for a compound when it reversibly sorbs between gas and atmospheric particulate phases? Two factors influence the answer. What physical mechanisms occur in the sorption process? What are the concentration and composition of atmospheric par...

  8. On Prognosis of Epitaxy from Gas Phase Process to Improve Properties of Epitaxial Layers

    NASA Astrophysics Data System (ADS)

    Pankratov, E. L.; Bulaeva, E. A.

    2015-12-01

    In this paper we analyzed mass and heat transport in a reactor from gas phase during growth an epitaxial layer. Based on results of the analysis we analyzed dependences of properties of grown layers on parameters of technological process.

  9. DETERMINATION OF CHLOROETHENES IN ENVIRONMENTAL BIOLOGICAL SAMPLES USING GAS CHROMATOGRAPHY COUPLED WITH SOLID PHASE MICRO EXTRACTION

    EPA Science Inventory

    An analytical method has been developed to determine the chloroethene series, tetrachloroethene (PCE), trichloroethene (TCE),cisdichloroethene (cis-DCE) andtransdichloroethene (trans-DCE) in environmental biotreatment studies using gas chromatography coupled with a solid phase mi...

  10. Gas-phase water-mediated equilibrium between methylglyoxal and its geminal diol

    PubMed Central

    Axson, Jessica L.; Takahashi, Kaito; De Haan, David O.; Vaida, Veronica

    2010-01-01

    In aqueous solution, aldehydes, and to a lesser extent ketones, hydrate to form geminal diols. We investigate the hydration of methylglyoxal (MG) in the gas phase, a process not previously considered to occur in water-restricted environments. In this study, we spectroscopically identified methylglyoxal diol (MGD) and obtained the gas-phase partial pressures of MG and MGD. These results, in conjunction with the relative humidity, were used to obtain the equilibrium constant, KP, for the water-mediated hydration of MG in the gas phase. The Gibbs free energy for this process, ?G, obtained as a result, suggests a larger than expected gas-phase diol concentration. This may have significant implications for understanding the role of organics in atmospheric chemistry. PMID:20142510

  11. Surface Nanobubbles Nucleate Microdroplets

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

    2014-04-01

    When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.

  12. How to control bubble nucleation from superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Giacomello, Alberto; Amabili, Matteo; Massimo Casciola, Carlo

    2015-12-01

    Superhydrophobicity is realized by entrapping gas bubbles inside surface roughness. While this strategy affords remarkable surface properties, it enhances the risk of cavitation from these gas nuclei at negative pressures. Here we use free energy molecular dynamics simulations and an extension of the classical nucleation theory to show that the relevant nucleation rates and barriers can be controlled by engineering the surface structure. Mimicking the re-entrant and chemically heterogeneous structure found in the leaves of the Salvinia molesta allows one both to stabilize the gas pockets against liquid intrusion and to reduce the risk of cavitation.

  13. Nucleation of metals by strong electric fields

    NASA Astrophysics Data System (ADS)

    Nardone, M.; Karpov, V. G.

    2012-04-01

    Recent work on phase transitions in chalcogenides (underlying phase change memory) led to a theory of symmetry-breaking field effects, predicting needle-shaped metallic nuclei and exponentially accelerated nucleation rates. Here, we predict that, in general, any insulator will eventually form metallic inclusions if immersed in a sufficient electric field. These phase transitions are driven, not simply enhanced, by an electric field. Hence, metals can be formed under conditions where they would be otherwise unexpected. This opens the venue of field induced materials synthesis. As a technologically important example, we consider the field driven synthesis of metallic hydrogen at normal pressure.

  14. Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase

    NASA Astrophysics Data System (ADS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Beno?t

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  15. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall,G.E.; Sears, T.J.

    2009-04-03

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

  16. An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill

    1988-01-01

    A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.

  17. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  18. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall G. E.; Goncharov, V.

    2012-05-29

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  19. Transient nucleation in condensed systems

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Greer, A. L.; Thompson, C. V.

    1983-01-01

    Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.

  20. Translational invariance in nucleation theories: Theoretical formulation

    SciTech Connect

    Drossinos, Y.; Kevrekidis, P. G.; Georgopoulos, P. G.

    2001-03-01

    The consequences of spontaneously broken translational invariance on the nucleation-rate statistical prefactor in theories of first-order phase transitions are analyzed. A hybrid, semiphenomenological approach based on field-theoretic analyses of condensation and modern density-functional theories of nucleation is adopted to provide a unified prescription for the incorporation of translational-invariance corrections to nucleation-rate predictions. A connection between these theories is obtained starting from a quantum-mechanical Hamiltonian and using methods developed in the context of studies on Bose-Einstein condensation. An extremum principle is used to derive an integro-differential equation for the spatially nonuniform mean-field order-parameter profile; the appropriate order parameter becomes the square root of the fluid density. The importance of the attractive intermolecular potential is emphasized, whereas the repulsive two-body potential is approximated by considering hard-sphere collisions. The functional form of the degenerate translational eigenmodes in three dimensions is related to the mean-field order parameter, and their contribution to the nucleation-rate prefactor is evaluated. The solution of the Euler-Lagrange variational equation is discussed in terms of either a proposed variational trial function or the complete numerical solution of the associated boundary-value integro-differential problem. Alternatively, if the attractive potential is not explicitly known, an approach that allows its formal determination from its moments is presented.

  1. Translational invariance in nucleation theories: theoretical formulation.

    PubMed

    Drossinos, Y; Kevrekidis, P G; Georgopoulos, P G

    2001-03-01

    The consequences of spontaneously broken translational invariance on the nucleation-rate statistical prefactor in theories of first-order phase transitions are analyzed. A hybrid, semiphenomenological approach based on field-theoretic analyses of condensation and modern density-functional theories of nucleation is adopted to provide a unified prescription for the incorporation of translational-invariance corrections to nucleation-rate predictions. A connection between these theories is obtained starting from a quantum-mechanical Hamiltonian and using methods developed in the context of studies on Bose-Einstein condensation. An extremum principle is used to derive an integro-differential equation for the spatially nonuniform mean-field order-parameter profile; the appropriate order parameter becomes the square root of the fluid density. The importance of the attractive intermolecular potential is emphasized, whereas the repulsive two-body potential is approximated by considering hard-sphere collisions. The functional form of the degenerate translational eigenmodes in three dimensions is related to the mean-field order parameter, and their contribution to the nucleation-rate prefactor is evaluated. The solution of the Euler-Lagrange variational equation is discussed in terms of either a proposed variational trial function or the complete numerical solution of the associated boundary-value integro-differential problem. Alternatively, if the attractive potential is not explicitly known, an approach that allows its formal determination from its moments is presented. PMID:11308725

  2. Formation of complex organic molecules in cold objects: the role of gas-phase reactions

    NASA Astrophysics Data System (ADS)

    Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

    2015-04-01

    While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ≳ 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

  3. Nucleated cells circulating in the peripheral blood contribute to the repair of osteochondral defects only in the early phase of healing.

    PubMed

    Okano, Tadashi; Wakitani, Shigeyuki; Okabe, Takahiro; Takahashi, Masafumi; Koike, Tatsuya; Nakamura, Hiroaki

    2014-05-01

    The role of cells circulating in the peripheral blood to participate in the natural repair process of osteochondral defects was evaluated in a green fluorescent protein (GFP) transgenic and wild rat parabiosis model. Two weeks after the parabiosis operation, vascular communication between the conjoined rats was confirmed by flow-cytometry analysis. A 1.5 mm diameter and 1.0 mm depth osteochondral defect was made in the patellar groove of each rat femoral bone. Histological examination was performed at 1, 2, 4 and 24 weeks following surgery. In the early postoperative phase (1-4 weeks) there were GFP-negative and -positive cells in the defects of both parabiotic rats. GFP-positive chondrocytes were confirmed partly in the repair tissue of the wild parabiotic rat. In the late postoperative phase (24 weeks), the repaired defects were occupied by cells originating from the adjacent tissue and not from the peripheral blood. The ratio of cells originating from the peripheral blood was approximately 30-40% in the repair tissue at 1 week after surgery, reduced to 0-7% at 24 weeks. From these results it is confirmed that cells circulating in the peripheral blood contributed to the repair of the osteochondral defects, particularly in the early phase of healing. Thus, peripheral blood not only supplies the factors needed for repair but also provides a cell population involved in the wound-healing process. PMID:22674849

  4. Constraining the Multi-Phase Gas Content of Galaxies in the Local Cosmic Web

    NASA Astrophysics Data System (ADS)

    Stark, David; Kannappan, S. J.; Wei, L. H.; Baker, A. J.; Haynes, M. P.; Giovanelli, R.; Heitsch, F.; RESOLVE Team; ALFALFA Team

    2010-01-01

    The RESOLVE (REsolved Spectroscopy Of a Local VolumE) Survey is a census of gas, stars, and dark matter in 1500 galaxies down to dwarf-scale baryonic masses of 109 Msun, occupying a range of cluster, group, and filament environments in the local cosmic web. We discuss strategies to estimate the gas mass in HI, H2, and warmer phases. RESOLVE falls largely within the footprint of the ongoing ALFALFA survey, allowing us to acquire accurate HI data for much of the sample. Any missing HI masses will be estimated from color and environment data, based on trends calibrated using the ALFALFA data set. Initially, our constraints on the molecular gas component will be largely indirect, based on either AKARI FIR data or a new technique presented here that links CO-derived H2/HI ratios to stellar-mass normalized color gradients. We discuss additional strategies under development to better measure molecular gas and constrain the mass in warmer phases. In particular, we describe observational constraints on the nature of additional gas that is detected dynamically in a sample of very blue, gas-dominated galaxies, possibly representing a warm-hot phase or a low-metallicity molecular component. Obtaining a full gas census for the RESOLVE survey will allow us to model gas phase transitions and star formation, specifically examining how baryonic mass component ratios and conversion timescales depend on galaxy mass and environment.

  5. DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.

    EPA Science Inventory

    The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

  6. Homogeneous nucleation of magnesium hydroxide.

    PubMed

    Klein, D H; Smith, M D; Driy, J A

    1967-08-01

    The rate of homogeneous nucleation of magnesium hydroxide has been determined as a function of solution concentration, using a quasi-homogeneous precipitation technique and electronic particle counting. The nucleation rate becomes measurable at super-saturations of about 4, and is dependent on the 33rd power of the product aMgaOH(2). The experimental results are consistent with nucleation theory. The nucleus-solution interfacial energy is calculated to be 115 erg/cm(2). PMID:18960187

  7. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    DOE PAGESBeta

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP)more » methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.« less

  8. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    SciTech Connect

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP) methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.

  9. Bubble nucleation in polymerCO2 mixtures.

    PubMed

    Xu, Xiaofei; Cristancho, Diego E; Costeux, Stphane; Wang, Zhen-Gang

    2013-10-28

    We combine density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in two polymerCO2 mixture systems, poly(methyl methacrylate) (PMMA)CO2 and polystyrene (PS)CO2. Nucleation is initiated by saturating the polymer liquid with high pressure CO2 and subsequently reducing the pressure to ambient condition. Below a critical temperature (Tc), we find that there is a discontinuous drop in the nucleation barrier as a function of increased initial CO2 pressure (P0), as a result of an underlying metastable transition from a CO2-rich-vapor phase to a CO2-rich-liquid phase. The nucleation barrier is generally higher for PSCO2 than for PMMACO2 under the same temperature and pressure conditions, and both higher temperature and higher initial pressure are required to lower the nucleation barrier for PSCO2 to experimentally relevant ranges. Classical nucleation theory completely fails to capture the structural features of the bubble nucleus and severely underestimates the nucleation barrier. PMID:26029777

  10. Seeding approach to crystal nucleation

    NASA Astrophysics Data System (ADS)

    Espinosa, Jorge R.; Vega, Carlos; Valeriani, Chantal; Sanz, Eduardo

    2016-01-01

    We present a study of homogeneous crystal nucleation from metastable fluids via the seeding technique for four different systems: mW water, Tosi-Fumi NaCl, Lennard-Jones, and Hard Spheres. Combining simulations of spherical crystal seeds embedded in the metastable fluid with classical nucleation theory, we are able to successfully describe the nucleation rate for all systems in a wide range of metastability. The crystal-fluid interfacial free energy extrapolated to coexistence conditions is also in good agreement with direct calculations of such parameter. Our results show that seeding is a powerful technique to investigate crystal nucleation.

  11. Seeding approach to crystal nucleation.

    PubMed

    Espinosa, Jorge R; Vega, Carlos; Valeriani, Chantal; Sanz, Eduardo

    2016-01-21

    We present a study of homogeneous crystal nucleation from metastable fluids via the seeding technique for four different systems: mW water, Tosi-Fumi NaCl, Lennard-Jones, and Hard Spheres. Combining simulations of spherical crystal seeds embedded in the metastable fluid with classical nucleation theory, we are able to successfully describe the nucleation rate for all systems in a wide range of metastability. The crystal-fluid interfacial free energy extrapolated to coexistence conditions is also in good agreement with direct calculations of such parameter. Our results show that seeding is a powerful technique to investigate crystal nucleation. PMID:26801035

  12. Phase transitions in a 3 dimensional lattice loop gas

    SciTech Connect

    MacKenzie, Richard; Nebia-Rahal, F.; Paranjape, M. B.

    2010-06-01

    We investigate, via Monte Carlo simulations, the phase structure of a system of closed, nonintersecting but otherwise noninteracting, loops in 3 Euclidean dimensions. The loops correspond to closed trajectories of massive particles and we find a phase transition as a function of their mass. We identify the order parameter as the average length of the loops at equilibrium. This order parameter exhibits a sharp increase as the mass is decreased through a critical value, the behavior seems to be a crossover transition. We believe that the model represents an effective description of the broken-symmetry sector of the 2+1 dimensional Abelian Higgs model, in the extreme strong coupling limit. The massive gauge bosons and the neutral scalars are decoupled, and the relevant low-lying excitations correspond to vortices and antivortices. The functional integral can be approximated by a sum over simple, closed vortex loop configurations. We present a novel fashion to generate nonintersecting closed loops, starting from a tetrahedral tessellation of three space. The two phases that we find admit the following interpretation: the usual Higgs phase and a novel phase which is heralded by the appearance of effectively infinitely long loops. We compute the expectation value of the Wilson loop operator and that of the Polyakov loop operator. The Wilson loop exhibits perimeter law behavior in both phases implying that the transition corresponds neither to the restoration of symmetry nor to confinement. The effective interaction between external charges is screened in both phases, however there is a dramatic increase in the polarization cloud in the novel phase as shown by the energy shift introduced by the Wilson loop.

  13. NANOMATERIAL SOLUTIONS FOR HOT COAL GAS CLEANUP - PHASE I

    EPA Science Inventory

    Integrated gasification combined cycle (IGCC) is a new coal gasification technique that efficiently uses the hot (900-1500C) generated syngas to power both steam and gas turbines. Due to regulations, this syngas must be free of sulfur and purification is normally carried ...

  14. NANOMATERIAL SOLUTIONS FOR HOT COAL GAS CLEANUP - PHASE I

    EPA Science Inventory

    Integrated gasification combined cycle (IGCC) is a new coal gasification technique that efficiently uses the hot (900-1500°C) generated syngas to power both steam and gas turbines. Due to regulations, this syngas must be free of sulfur and purification is normally carried ...

  15. AN ADVANCED FLUE GAS MONITOR FOR SO2 - PHASE I

    EPA Science Inventory

    The development of an instrument for continuously monitoring SO2 levels in flue gas is proposed. The SO2 will be detected by means of an electrochemical sensor cell, which operates in a three-electrode potentiostatic mode. The proposed innovation is develop-ment of an advan...

  16. Ceramic stationary gas turbine development. Final report, Phase 1

    SciTech Connect

    1994-09-01

    This report summarizes work performed by Solar Turbines Inc. and its subcontractors during the period September 25, 1992 through April 30, 1993. The objective of the work is to improve the performance of stationary gas turbines in cogeneration through implementation of selected ceramic components.

  17. Eastern gas shales mineback report: site assessment - Phase I

    SciTech Connect

    Overbey, W.K.; Sawyer, W.K.; Shuck, K.Z.; Zielinski, R.E.

    1981-01-01

    The technology development and demonstration program herein described resulted from an assessment of the state-of-the-art problems of gas recovery, from the Eastern Devonian Shales. After ten years of Devonian Shale research, the remaining major issues for developing the shale resource have been defined and this project was formulated to address those specific recovery problems. This document provides the rationale and criteria for selecting and evaluating a site for a mineback type project and the experimental results obtained from a one hundred and twenty day on-site testing and evaluation plan. The site selected as the best overall candidate for on-site testing was Sugarloaf Mountain, which is located about six miles off the Interstate I-64 exit at Morehead, Kentucky. The on-site testing included obtaining a core through the Ohio shale interval, core analysis, in-situ stress measurements from five boreholes, gas pressure buildup, natural fracture and joint mapping, hydraulic fracture orientation mapping, photogeology and a thorough study of the geology and gas shale reservoir history in the area. Results of the site evaluation data obtained to date indicate the site to be a very favorable one for conducting the planned mineback experiments and future development, testing and demonstration of Devonian Gas shales recovery technology.

  18. Gas phase dispersion in a small rotary kiln

    SciTech Connect

    Spencer, B.B.

    1981-07-01

    A study was made of nonideal flow of gas in a rotary kiln reactor. A rotating tube 0.165 m in diameter by 2.17 m long, with internal lifting flights, was operated at room temperature. Rotational speeds from 2.0 to 7.0 rpm, air flow rates from 0.351 to 4.178 m/sup 3//h, and solid contents of 0.0, 5.1, and 15.3% of tube volume were studied. Residence time distribution of the gas was measured by means of the pulse injection technique using a helium tracer. A model was developed based on dispersive flow that exchanges with a deadwater region. Two parameters, a dispersion number describing bulk gas flow and an interchange factor describing exchange between the flow region and the gas trapped in the solids bed, were sufficient to correlate the data, but these parameters are sensitive to experimental error. The model is applicable to analysis of other flow systems, such as packed beds.

  19. A phenomenological theory of nonphotochemical laser induced nucleation.

    PubMed

    Nardone, Marco; Karpov, Victor G

    2012-10-21

    We present a theory of electric field driven phase transitions that occur via nucleation of needle-shaped, metallic particles. The predictions of this theory have much in common with the observations related to nonphotochemical laser induced nucleation (NPLIN). That connection is rather paradoxical because the final NPLIN products are dielectric crystals. By elaborating on the unique features of field induced transitions and the complexities of liquid systems, we discuss how our theory may provide some insight into the open question of the NPLIN mechanism. A qualitative description of the post nucleation stage and conjectures about the microscopic nature of the metallic particles in liquids are also provided. PMID:22955565

  20. In Situ Investigations into CaCO3 Nucleation

    NASA Astrophysics Data System (ADS)

    Nielsen, Michael Harold

    Classical theories of nucleation were developed over a hundred years ago starting with Gibbs. However, much remains unknown about the process of phase transition in aqueous electrolyte solutions due to the lack of experimental tools able to probe dynamic processes at the time and length scales of the phase transformation. In the calcium carbonate system, recent discovery of an amorphous phase, as well as the suggested existence of potential precursor states such as so-called 'pre-nucleation clusters' or dense liquid droplets, has called into question the utility of the classical framework in making accurate predictions of nucleation. Added to these questions are those regarding the effects that chemical templates have on nucleating calcium carbonate. Many organisms use complex organic matrices to form architecturally complex functional structures out of sea water at ambient temperatures. By contrast, laboratory methods to materials synthesis often require extreme conditions yet maintain at best a low level of control over the development of the resulting material. With the goal of tightly controlling formation of functional materials, scientists have looked to such biomineral systems for inspiration. Self-assembled monolayers (SAMs) of functionalized alkanethiols have been found to act as idealized chemical templates for calcium carbonate nucleation, controlling the nucleating plane of the calcite phase for many surface functionalities. Yet there remain many open questions as to the fundamental mechanisms by which these templates achieve this control. In this dissertation many investigations of calcium carbonate nucleation are discussed, which examine the nucleation pathways of calcium carbonate and mechanisms of control by which alkanethiol surfaces direct the oriented formation of calcite. Traditional in situ microscopy techniques are used to make nucleation rate measurements of templated calcite nucleation on alkanethiol SAMs to test the applicability of the predictions of classical nucleation theory to this system. Low resolution microscopy techniques are further used to provide indirect evidence for the formation pathways of calcite on SAMs exhibiting different surface chemistries. The development of a platform for liquid phase transmission electron microscopy (TEM) utilizing a sealed liquid cell is described, and its utility in making novel observations of materials formation processes is demonstrated. Liquid phase TEM is further employed, using an open cell system which allows for mixing reagents, to directly observe formation pathways in the CaCO3 system.

  1. Gas phase condensation of superparamagnetic iron oxide-silica nanoparticles - control of the intraparticle phase distribution

    NASA Astrophysics Data System (ADS)

    Stötzel, C.; Kurland, H.-D.; Grabow, J.; Müller, F. A.

    2015-04-01

    Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis. Electronic supplementary information (ESI) available: Infrared absorption of the raw powders hematite and quartz (section S1), TEM investigation of the spatial distribution of the γ-Fe2O3 inclusions (section S2), particle size distributions of the Fe2O3@SiO2 nanopowder samples (section S3), ζ-potentials of aqueous dispersions of all γ-Fe2O3@SiO2 nanopowder samples (section S4), silanization of Fe2O3@SiO2 composite nanopowders with [3-(2,3-epoxypropoxy)-propyl]trimethoxysilane (section S5), and animation composed of TEM micrographs of Fe2O3@SiO2 NPs recorded at incrementally altered tilt angles (``Rotating Fe2O3@SiO2 NP.avi''). See DOI: 10.1039/c5nr00845j

  2. Kinetics of nucleation with decreasing rate of growth

    NASA Astrophysics Data System (ADS)

    Kurasov, Victor

    2015-10-01

    Extension of analytical description of the stage of nucleation to the case of the slow growth rates of the embryos growth has been constructed. The metastable phase consumption by the already formed embryos affects the nucleation rate which leads to the non-linear evolution. The power exponentials which are smaller than that for the diffusion growth are chosen as the model laws of the embryos growth. All main characteristics of the nucleation period including the form of the embryos sizes spectrum are found. Analytical description of nucleation in the closed systems as well as in the open systems with the metastable phase influx is presented. It is shown that the relative errors of this description are small.

  3. Separation of gas from liquid in a two-phase flow system

    NASA Technical Reports Server (NTRS)

    Hayes, L. G.; Elliott, D. G.

    1973-01-01

    Separation system causes jets which leave two-phase nozzles to impinge on each other, so that liquid from jets tends to coalesce in center of combined jet streams while gas phase is forced to outer periphery. Thus, because liquid coalescence is achieved without resort to separation with solid surfaces, cycle efficiency is improved.

  4. ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA

    EPA Science Inventory

    The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

  5. Pore network modeling of two-phase flow in a liquid-(disconnected) gas system

    NASA Astrophysics Data System (ADS)

    Bravo, Maria C.; Araujo, Mariela; Lago, Marcelo E.

    2007-02-01

    The appropriate description of two-phase flow in some systems requires a detailed analysis of the fundamental equations of flow and transport including momentum transfer between fluid phases. In the particular case of two-phase flow of oil and gas through porous media, when the gas phase is present as disconnected bubbles, there are inconsistencies in calculated flow properties derived by using the conventional Darcean description. In a two-phase system, the motion of one fluid phase may induce significant changes in the mobility of the second phase, as known from the generalized transport equations derived by Whitaker and Kalaydjian. The relevance of such coupling coefficients with respect to the conventional relative permeability term in two-phase Darcean flow is evaluated in this work for an oil-(disconnected) gas system. The study was performed using a new Pore Network Simulator specially designed for this case. Results considering both, Darcy's equation and generalized flow equations suggest that the four transport coefficients (effective permeabilities and coupling coefficients) are needed for a proper description of the macroscopic flow in a liquid-disconnected gas system.

  6. Positron annihilation in benzene and cyclohexane: a comparison between gas and liquid phase

    NASA Astrophysics Data System (ADS)

    Fedus, Kamil

    2015-06-01

    A comparative study about positron annihilation in gas and liquid phases of two non-polar ring molecules: benzene (C6H6) and cyclohexane (C6H12) is presented including the most recent experimental and theoretical achievements. In addition the preliminary results of positron annihilation lifetime measurements in a liquid phase at room temperature for these two molecules are reported.

  7. Bridging the Gap between the Gas Phase and Solution Phase: Solvent Specific Photochemistry in 4-tert-Butylcatechol.

    PubMed

    Horbury, Michael D; Baker, Lewis A; Quan, Wen-Dong; Young, Jamie D; Staniforth, Michael; Greenough, Simon E; Stavros, Vasilios G

    2015-12-17

    Eumelanin is a naturally synthesized ultraviolet light absorbing biomolecule, possessing both photoprotective and phototoxic properties. We infer insight into these properties of eumelanin using a bottom-up approach, by investigating an ultraviolet absorbing motif of eumelanin, 4-tert-butylcatechol. Utilizing a combination of femtosecond transient electronic absorption spectroscopy and time-resolved velocity map ion imaging, our results suggest an environmental-dependent relaxation pathway, following irradiation at 267 nm to populate the S1 ((1)??*) state. Gas-phase and nonpolar solution-phase measurements reveal that the S1 state decays primarily through coupling onto the S2 ((1)??*) state which is dissociative along the nonintramolecular hydrogen bonded "free" O-H bond. This process occurs in 4.9 0.6 ps in the gas-phase and 18 1 ps in the nonpolar cyclohexane solution. Comparative studies on the deuterated isotopologue of 4-tert-butylcatechol in both the gas- and solution-phase (cyclohexane) reveal kinetic isotope effects of ?19 and ?4, respectively, supportive of O-H dissociation along a barriered pathway, and potentially mediated by quantum tunneling. In contrast, in the polar solvent acetonitrile, the S1 state decays on a much longer time scale of 1.7 0.1 ns. We propose that the S1 decay is now multicomponent, driven by internal conversion, intersystem crossing, and fluorescence, as well as O-H dissociation. The attribution of conformer-driven excited state dynamics to explain how the S1 state decays in the gas- and nonpolar solution-phase versus the polar solution-phase, demonstrates the influence the environment can have on the ensuing excited state dynamics. PMID:26015078

  8. Identification of Ice Nucleation Active Sites on Silicate Dust Particles

    NASA Astrophysics Data System (ADS)

    Zolles, Tobias; Burkart, Julia; Husler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich

    2015-04-01

    Mineral dusts originating from Earth's crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts [1-3]. Nevertheless, among those structures K-feldspar showed by far the highest ice nucleation activity. In this study, the reasons for its activity and the difference in the activity of the different feldspars were investigated in closer details. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. We give a potential explanation of the increased ice nucleation activity of K-feldspar. The ice nucleating sites are very much dependent on the alkali ion present by altering the water structure and the feldspar surface. The higher activity of K-feldspar can be attributed to the presence of potassium ions on the surface and surface bilayer. The alkali-ions have different hydration shells and thus an influence on the ice nucleation activity of feldspar. Chaotropic behavior of Calcium and Sodium ions are lowering the ice nucleation potential of the other feldspars, while kosmotropic Potassium has a neutral or even positive effect. Furthermore we investigated the influence of milling onto the ice nucleation of quartz particles. The ice nucleation activity can be increased by mechanical milling, by introducing more molecular, nucleation active defects to the particle surface. This effect is larger than expected by plane surface increase. [1] Atkinson et al. The Importance of Feldspar for Ice Nucleation by Mineral Dust in Mixed-Phase Clouds. Nature 2013, 498, 355-358. [2] Yakobi-Hancock et al.. Feldspar Minerals as Efficient Deposition Ice Nuclei. Atmos. Chem. Phys. 2013, 13, 11175-11185. [3] Zolles et al. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles. J. Phys. Chem. A 2015 accepted.

  9. Probing methane hydrate nucleation through the forward flux sampling method.

    PubMed

    Bi, Yuanfei; Li, Tianshu

    2014-11-26

    Understanding the nucleation of hydrate is the key to developing effective strategies for controlling methane hydrate formation. Here we present a computational study of methane hydrate nucleation, by combining the forward flux sampling (FFS) method and the coarse-grained water model mW. To facilitate the application of FFS in studying the formation of methane hydrate, we developed an effective order parameter ? on the basis of the topological analysis of the tetrahedral network. The order parameter capitalizes the signature of hydrate structure, i.e., polyhedral cages, and is capable of efficiently distinguishing hydrate from ice and liquid water while allowing the formation of different hydrate phases, i.e., sI, sII, and amorphous. Integration of the order parameter ? with FFS allows explicitly computing hydrate nucleation rates and obtaining an ensemble of nucleation trajectories under conditions where spontaneous hydrate nucleation becomes too slow to occur in direct simulation. The convergence of the obtained hydrate nucleation rate was found to depend crucially on the convergence of the spatial distribution for the spontaneously formed hydrate seeds obtained from the initial sampling of FFS. The validity of the approach is also verified by the agreement between the calculated nucleation rate and that inferred from the direct simulation. Analyzing the obtained large ensemble of hydrate nucleation trajectories, we show hydrate formation at 220 K and 500 bar is initiated by the nucleation events occurring in the vicinity of water-methane interface, and facilitated by a gradual transition from amorphous to crystalline structure. The latter provides the direct support to the proposed two-step nucleation mechanism of methane hydrate. PMID:24849698

  10. Liquid to solid nucleation via onion structure droplets

    NASA Astrophysics Data System (ADS)

    Barros, Kipton; Klein, W.

    2013-11-01

    We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions d ? 3 is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.

  11. Gas phase composition effects on suspension cultures of Taxus cuspidata

    SciTech Connect

    Mirjalili, N.; Linden, J.C.

    1995-10-20

    The effect of different concentrations and combinations of oxygen, carbon dioxide, and ethylene on cell growth and taxol production in suspension cultures of Taxus cuspidata was investigated using several factorial design experiments. Low head space oxygen concentration (10% v/v) promoted early production of taxol. High carbon dioxide concentration (10% v/v) inhibited taxol production.The most effective gas mixture composition in terms of taxol production was 10% (v/v) oxygen, 0.5% (v/v) carbon dioxide, and 5 ppm ethylene. Cultures grown under ambient concentration of oxygen had a delayed uptake of glucose and fructose compared to cultures grown under 10% (v/v) oxygen. Average calcium uptake rates into the cultured cells decreased and average phosphate uptake rates increased as ethylene was increased from 0 to 10 ppm. These results may indicate that gas composition alters partitioning of nutrients, which in turn affects secondary metabolite production.

  12. Gas distribution equipment in hydrogen service - Phase II

    NASA Technical Reports Server (NTRS)

    Jasionowski, W. J.; Huang, H. D.

    1980-01-01

    The hydrogen permeability of three different types of commercially available natural gas polyethylene pipes was determined. Ring tensile tests were conducted on permeability-exposed and as-received samples. Hydrogen-methane leakage experiments were also performed. The results show no selective leakage of hydrogen via Poiseuille, turbulent, or orifice flow (through leaks) on the distribution of blends of hydrogen and methane. The data collected show that the polyethylene pipe is 4 to 6 times more permeable to hydrogen than to methane.

  13. Spectroscopic studies of kinetically trapped conformations in the gas phase: the case of triply protonated bradykinin.

    PubMed

    Voronina, Liudmila; Rizzo, Thomas R

    2015-10-21

    Understanding the relation between the gas-phase structure of biological molecules and their solution-phase structure is important when attempting to use gas-phase techniques to address biologically relevant questions. Directly after electrospray ionization, molecules can be kinetically trapped in a state that retains some "memory" of its conformation in solution and is separated from the lowest-energy gas-phase structure by barriers on the potential energy surface. In order to identify and characterize kinetically trapped structures, we have explored the conformational space of triply protonated bradykinin in the gas phase by combining field-asymmetric ion mobility spectrometry (FAIMS) with cold ion spectroscopy. We isolate three distinct conformational families and characterize them by recording their UV-photofragment spectra and vibrational spectra. Annealing of the initial conformational distribution produced by electrospray reveals that one of the conformational families is kinetically trapped, while two others are stable, gas-phase structures. We compare our results to previously published results obtained using drift-tube ion mobility spectrometry (IMS) and propose a correspondence between the conformational families separated by FAIMS and those by IMS. PMID:25940085

  14. Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

    SciTech Connect

    Lin, Manhua; Wang, Xiang; Yeom, Younghoon

    2015-09-29

    A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase is dispersed.

  15. Liquid Gas Phase Transition for Asymmetric Nuclear Matter in the Zimanyi Moszkowski Model

    NASA Astrophysics Data System (ADS)

    Zhang, Xu-Ming; Qian, Wei-Liang; Su, Ru-Keng

    2004-07-01

    By using the improved Zimanyi-Moszkowski (ZM) model including the freedom of nucleons, sigma mesons, omega mesons and rho mesons, we investigate the liquid-gas phase transition for asymmetric nuclear matter. It is found that the phase transition for asymmetric nuclear matter in the improved ZM model with the isospin vector rho meson degree of freedom is well defined. The binodal surface, which is essential in the study of the phase transition process, is addressed.

  16. Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

    DOEpatents

    Lin, Manhua; Wang, Xiang; Yeom, Younghoon

    2015-03-17

    A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase id dispersed.

  17. Analysis of volatile phase transport in soils using natural radon gas as a tracer

    SciTech Connect

    Chen, C.; Thomas, D.M.

    1992-12-31

    We have conducted a field study of soil gas transport processes using radon gas as a naturally occurring tracer. The .experiment monitored soil gas radon activity, soil moisture, and soil temperature at three depths in the shallow soil column; barometric pressure, rainfall and wind speed were monitored at the soil surface. Linear and multiple regression analysis of the data sets has shown that the gas phase radon activities under natural environmental conditions are influenced by soil moisture content, barometric pressure variations, soil temperature and soil structure. The effect of wind speed on subsurface radon activities under our field conditions has not been demonstrated.

  18. Two-phase turbine engines. [using gas-liquid mixture accelerated in nozzles

    NASA Technical Reports Server (NTRS)

    Elliott, D. G.; Hays, L. G.

    1976-01-01

    A description is given of a two-phase turbine which utilizes a uniform mixture of gas and liquid accelerated in nozzles of the types reported by Elliott and Weinberg (1968). The mixture acts directly on an axial flow or tangential impulse turbine or is separated into gas and liquid streams which operate separately on a gas turbine and a hydraulic turbine. The basic two-phase cycles are examined, taking into account working fluids, aspects of nozzle expansion, details of turbine cycle operation, and the effect of mixture ratio variation. Attention is also given to two-phase nozzle efficiency, two-phase turbine operating characteristics and efficiencies, separator turbines, and impulse turbine experiments.

  19. Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity

    NASA Astrophysics Data System (ADS)

    Crews, Jackson B.; Cooper, Clay A.

    2014-09-01

    Changes in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 15 cm and 23 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.

  20. On Capillary Rise and Nucleation

    ERIC Educational Resources Information Center

    Prasad, R.

    2008-01-01

    A comparison of capillary rise and nucleation is presented. It is shown that both phenomena result from a balance between two competing energy factors: a volume energy and a surface energy. Such a comparison may help to introduce nucleation with a topic familiar to the students, capillary rise. (Contains 1 table and 3 figures.)